Modern computer software offers a variety of methods for specifying the colors of items to be drawn on a monitor; perhaps the best known of all is the red-green-blue model. This is certainly the direct approach, because within the hardware of nearly all color computer displays each pixel is divided into three subpixels, one red, one green, and one blue. Why three colors? The answer is derived from the fact that most human beings exhibit vision that is trichromatic, the eye having three types of cones each sensitive to a different range of wavelengths of light.

To use other than three colors in display design is possible. Some researchers have proposed using more than three colors to achieve a more faithful rendition. Meanwhile, advertisers sometimes erect large (measured in square meters) two-color display signs along major highways, using red and green subpixels but omitting blue. However, these non-tricolor implementations will be not investigated in this report.

In most display equipment, the color of a subpixel is determined by the substances of which it is made, with different chemicals emitting different wavelengths. Because many light-emissive materials are available, an engineer can select among several candidate reds, several greens, and several blues. Naturally, the engineer wants the equipment to be able to produce as many different colors as possible, but this must be balanced against matters such as the cost of materials and the consumption of power. For practical reasons then, no display purports to generate all the extremes of color perceivable by a human with normal vision — see sRGB for an example of the limitations. Further, real-world equipment is limited in granularity: in other words, a display might not be able to show both of two colors which are very nearly the same but still distinguishable by a human. Finally, color perception varies from person to person.

Subpixels on the typical computer monitor are so small that to a human viewing the screen from a normal distance (30 cm or more) they seem to merge. Even more, the pixels themselves are often so small that they too merge with one another. By contrast, many displays built before 1980 had pixels so coarse that they were readily discernable to a human viewer at normal distance.

The brightness of each subpixel can be controlled independently, yielding a broad assortment of colors. For instance, if a pixel's red subpixel is lit at full brightness, its green at mid-brightness, and its blue is turned off, an orange color will result. Because the human perception of brightness is not related in a simple way to the power supplied to a subpixel, some equipment uses correction techniques to make colors seem evenly spaced.

Application software frequently offers other ways to specify colors that are ultimately converted to red, green, and blue intensities — a well-known system is hue-saturation-brightness. Also, many applications allow the user to indicate red, green and blue intensities for images to be printed, even though those images are ultimately translated to some other color model, perhaps cyan-magenta-yellow-black.

Computer systems built since the year 2000 frequently support 256 levels of intensity for each of the subpixels; this number was selected for two reasons. The first is a matter of convenience: most computer hardware organizes storage into bytes, and a byte can contain 256 different values. The second is a matter of sufficiency: 256 brightness levels in each of red, green and blue gives a color space that is widely regarded as satisfactory because it produces a large and useful subset of the range of those colors that the human eye can detect, with granularity that approximates the distinguishing power of the human eye.

Because the red, green, and blue intensities can be specified separately, a table of all the colors that a particular computer screen can realize (the gamut) would naturally arrange itself into a three-dimensional figure. However, a computer screen has only two dimensions, so some compromise must be made in portraying the display's gamut on the display itself. The approach chosen for this report is to place the monitor colors into a cube, and then to slice the cube in a number of directions to obtain various cross sections. Included are oblique sections, which rarely appear in other web sites that dissect the color cube — one of the few is from Will Johnston.

Table two, near the bottom of this page, contains links to a number of charts containing slices of the color cube. Assumed throughout is that each of the red, green, and blue intensities is stored in one byte, and hence has 256 possible values. Zero denotes a subpixel that is completely dark, and 255 a pixel at maximum brightness, with intermediate numbers for intermediate brightnesses.

A complication must be addressed, because in computer science there are two oft-used ways of expressing numbers, and both appear widely in color specifications. One method is decimal notation, which is surely familiar to the reader; the alternative is hexadecimal, which is convenient for many computer purposes because it corresponds closely to the bits at the heart of computer storage. Table one, immediately below, is a conversion chart between hexadecimal integer, decimal integer, and decimal percentage. For instance, 43 in hexadecimal equals 67 in decimal, and can also be denoted as 26.27 percent. In bold are boxes containing hexadecimal numbers with repeated digits; these values are convenient, but not requisite, for specifying colors.

Table one.
Hexadecimal top Decimal middle Percentage bottom
00 0 0.00	01 1 0.39	02 2 0.78	03 3 1.18	04 4 1.57	05 5 1.96	06 6 2.35	07 7 2.75	08 8 3.14	09 9 3.53	0A 10 3.92	0B 11 4.31	0C 12 4.71	0D 13 5.10	0E 14 5.49	0F 15 5.88
10 16 6.27	11 17 6.67	12 18 7.06	13 19 7.45	14 20 7.84	15 21 8.24	16 22 8.63	17 23 9.02	18 24 9.41	19 25 9.80	1A 26 10.20	1B 27 10.59	1C 28 10.98	1D 29 11.37	1E 30 11.76	1F 31 12.16
20 32 12.55	21 33 12.94	22 34 13.33	23 35 13.73	24 36 14.12	25 37 14.51	26 38 14.90	27 39 15.29	28 40 15.69	29 41 16.08	2A 42 16.47	2B 43 16.86	2C 44 17.25	2D 45 17.65	2E 46 18.04	2F 47 18.43
30 48 18.82	31 49 19.22	32 50 19.61	33 51 20.00	34 52 20.39	35 53 20.78	36 54 21.18	37 55 21.57	38 56 21.96	39 57 22.35	3A 58 22.75	3B 59 23.14	3C 60 23.53	3D 61 23.92	3E 62 24.31	3F 63 24.71
40 64 25.10	41 65 25.49	42 66 25.88	43 67 26.27	44 68 26.67	45 69 27.06	46 70 27.45	47 71 27.84	48 72 28.24	49 73 28.63	4A 74 29.02	4B 75 29.41	4C 76 29.80	4D 77 30.20	4E 78 30.59	4F 79 30.98
50 80 31.37	51 81 31.76	52 82 32.16	53 83 32.55	54 84 32.94	55 85 33.33	56 86 33.73	57 87 34.12	58 88 34.51	59 89 34.90	5A 90 35.29	5B 91 35.69	5C 92 36.08	5D 93 36.47	5E 94 36.86	5F 95 37.25
60 96 37.65	61 97 38.04	62 98 38.43	63 99 38.82	64 100 39.22	65 101 39.61	66 102 40.00	67 103 40.39	68 104 40.78	69 105 41.18	6A 106 41.57	6B 107 41.96	6C 108 42.35	6D 109 42.75	6E 110 43.14	6F 111 43.53
70 112 43.92	71 113 44.31	72 114 44.71	73 115 45.10	74 116 45.49	75 117 45.88	76 118 46.27	77 119 46.67	78 120 47.06	79 121 47.45	7A 122 47.84	7B 123 48.24	7C 124 48.63	7D 125 49.02	7E 126 49.41	7F 127 49.80
80 128 50.20	81 129 50.59	82 130 50.98	83 131 51.37	84 132 51.76	85 133 52.16	86 134 52.55	87 135 52.94	88 136 53.33	89 137 53.73	8A 138 54.12	8B 139 54.51	8C 140 54.90	8D 141 55.29	8E 142 55.69	8F 143 56.08
90 144 56.47	91 145 56.86	92 146 57.25	93 147 57.65	94 148 58.04	95 149 58.43	96 150 58.82	97 151 59.22	98 152 59.61	99 153 60.00	9A 154 60.39	9B 155 60.78	9C 156 61.18	9D 157 61.57	9E 158 61.96	9F 159 62.35
A0 160 62.75	A1 161 63.14	A2 162 63.53	A3 163 63.92	A4 164 64.31	A5 165 64.71	A6 166 65.10	A7 167 65.49	A8 168 65.88	A9 169 66.27	AA 170 66.67	AB 171 67.06	AC 172 67.45	AD 173 67.84	AE 174 68.24	AF 175 68.63
B0 176 69.02	B1 177 69.41	B2 178 69.80	B3 179 70.20	B4 180 70.59	B5 181 70.98	B6 182 71.37	B7 183 71.76	B8 184 72.16	B9 185 72.55	BA 186 72.94	BB 187 73.33	BC 188 73.73	BD 189 74.12	BE 190 74.51	BF 191 74.90
C0 192 75.29	C1 193 75.69	C2 194 76.08	C3 195 76.47	C4 196 76.86	C5 197 77.25	C6 198 77.65	C7 199 78.04	C8 200 78.43	C9 201 78.82	CA 202 79.22	CB 203 79.61	CC 204 80.00	CD 205 80.39	CE 206 80.78	CF 207 81.18
D0 208 81.57	D1 209 81.96	D2 210 82.35	D3 211 82.75	D4 212 83.14	D5 213 83.53	D6 214 83.92	D7 215 84.31	D8 216 84.71	D9 217 85.10	DA 218 85.49	DB 219 85.88	DC 220 86.27	DD 221 86.67	DE 222 87.06	DF 223 87.45
E0 224 87.84	E1 225 88.24	E2 226 88.63	E3 227 89.02	E4 228 89.41	E5 229 89.80	E6 230 90.20	E7 231 90.59	E8 232 90.98	E9 233 91.37	EA 234 91.76	EB 235 92.16	EC 236 92.55	ED 237 92.94	EE 238 93.33	EF 239 93.73
F0 240 94.12	F1 241 94.51	F2 242 94.90	F3 243 95.29	F4 244 95.69	F5 245 96.08	F6 246 96.47	F7 247 96.86	F8 248 97.25	F9 249 97.65	FA 250 98.04	FB 251 98.43	FC 252 98.82	FD 253 99.22	FE 254 99.61	FF 255 100.00

Each color sample in the charts bears a legend similar to this one:

	A2 2E 00

These hexadecimal numbers mean that the red intensity is A2, green is 2E, and blue is 00. Decimal equivalents are 162, 46, and 0 respectively. As percentages of the maximum, they would be calculated as 63.53, 18.04, and 0.00.

In the 2-, 4- and 6-level charts of table two, the hexadecimal notations for the intensities happen to use repeated digits. In contrast, the 12-level charts contain little repetition. Within each chart, the intensities are spaced as evenly as possible from a numerical point of view; they may not seem evenly spaced to the eye, depending on the equipment on which the colors are viewed. Only a few of the 16,777,216 possible colors are included in the charts of table two, but the ones that do appear (especially in the 12-level charts) should help a graphical designer infer what the others look like.

Table two.
Orientation	Starting and ending colors	2 Levels	4 Levels	6 Levels	12 Levels
Face to Face Each slice is parallel to some face of the cube.	Blk-Red-Blu-Mag to Grn-Yel-Cyn-Wht	2 pages	4 pages	6 pages	12 pages
	Blk-Grn-Red-Yel to Blu-Cyn-Mag-Wht	2 pages	4 pages	6 pages	12 pages
	Blk-Blu-Grn-Cyn to Red-Mag-Yel-Wht	2 pages	4 pages	6 pages	12 pages
Edge to Edge Each slice is parallel to some edge of the cube, and perpendicular to a diagonal of some face of the cube.	Blk-Red to Cyn-Wht	3 pages	7 pages	11 pages	23 pages
	Blk-Grn to Mag-Wht	3 pages	7 pages	11 pages	23 pages
	Blk-Blu to Yel-Wht	3 pages	7 pages	11 pages	23 pages
	Red-Yel to Blu-Cyn	3 pages	7 pages	11 pages	23 pages
	Blu-Mag to Grn-Yel	3 pages	7 pages	11 pages	23 pages
	Grn-Cyn to Red-Mag	3 pages	7 pages	11 pages	23 pages
Corner to Corner Each slice is perpendicular to a diagonal of the body of the cube.	Blk to Wht	4 pages	10 pages	16 pages	34 pages
	Cyn to Red	4 pages	10 pages	16 pages	34 pages
	Mag to Grn	4 pages	10 pages	16 pages	34 pages
	Yel to Blu	4 pages	10 pages	16 pages	34 pages

Here are the color abbreviations:

Blk Black	Red Red	Grn Green	Blu Blue	Yel Yellow	Mag Magenta	Cyn Cyan	Wht White

The 6-level charts above contain what have been called the "browser-safe" colors. Many computers of the 1990s were limited by their hardware to rendering only 256 colors, and had to use dithering to simulate other colors. Typical machines included all 216 colors of the 6 x 6 x 6 color cube among the 256, and used the remaining 40 for system-specific purposes.

An example is the default palette of AppleWorks version 6.2.9. This collection includes all 216 of the 6-level colors, plus extra grays, reds, greens and blues. All 256 of these colors can be written with double digits in hexadecimal. The irregular arrangement in this chart reflects the difficulty in finding an orderly way to display the color cube in only two dimensions.