Chapter 16. Specifying Color in HTML
You can specify the color of certain page elements using HTML tags. There are two methods for specifying colors in web documents: RGB values and color name.
16.1. Specifying Color by RGB Values
The most common and precise way to specify a color in HTML is by its numerical RGB (red, green, blue) values. For an explanation of RGB color, see Section 3.3, "Color on the Web" in Chapter 3, "Web Design Principles for Print Designers".
Once you've identified the red, green, and blue values of your chosen color (an image-editing tool helps with this task), you need to translate them to their hexadecimal equivalents in order to enter them into the HTML color tag. These values are written in HTML with the following syntax:
"#RRGGBB"
RR stands for the hexadecimal red value, GG stands for the hexadecimal green value, and BB stands for the hexadecimal blue value. Using these values, you can specify any color from the "true color" space (millions of colors).
Let's look at an example to put this in context. To set the background color of a document to dark olive green, first find the RGB values of the color (85, 107, 47) and convert them into their hexadecimal equivalents (55, 6B, 2F; explanation of conversion follows). Then the values can be placed in an HTML tag, in this case to change the background color of a page:
<BODY BGCOLOR="#556B2F">
16.1.1. The Hexadecimal System
The hexadecimal numbering system is base-16 (as compared to base-10 for decimal numbers). It uses the following 16 characters:
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F
A through F represent the decimal values 10 through 15.
16.1.2. Converting Decimal to Hexadecimal
You can calculate hex values in the 0 to 255 range by dividing a number by 16 to get the first digit, then using the remainder for the second digit. For example, dividing the decimal number 203 by 16 yields 12 with a remainder of 11. The hexadecimal value of 12 is C; the hex value of 11 is B. Therefore, the hexadecimal equivalent of 203 is CB.
Fortunately, there are simpler methods for converting numbers to hexadecimal:
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Use Table 16-1, which translates decimal values from 0 to 255.
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Use a hexadecimal calculator. On the Macintosh, you can download a copy of a utility called Calculator II (ftp://ftp.amug.org/pub/mirrors/info-mac/sci/calc/calculator-ii-15.hqx). Windows users can find a hexadecimal calculator in the "Scientific" view of the Windows standard calculator.
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Use online resources. There are several resources online for calculating hexadecimal equivalents. Some allow you to enter all three values for red, green, and blue, and convert to hexadecimal while showing you a sample of your chosen color immediately. Examples of online calculations include:
- Mediarama's Color Page Builder
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Plug in your decimal RGB values for page elements, and this page automatically generates a sample page with your color selections and the HTML code for the <body> tag. See http://www.inquisitor.com/hex.html.
- URL Univox Internet: RGB 2 Hex
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This is a stripped-down, no-frills tool for converting decimal RGB values to their hex equivalents. See http://www.univox.com/rgb2hex.html.
Table 16-1. Decimal to hexadecimal equivalents
|
dec = hex |
dec = hex |
dec = hex |
dec = hex |
dec = hex |
dec = hex |
dec = hex |
dec = hex |
dec = hex |
dec = hex |
dec = hex |
dec = hex |
|---|---|---|---|---|---|---|---|---|---|---|---|
|
0 = 00 1 = 01 2 = 02 3 = 03 4 = 04 5 = 05 6 = 06 7 = 07 8 = 08 9 = 09 10 = 0A 11 = 0B 12 = 0C 13 = 0D 14 = 0E 15 = 0F 16 = 10 17 = 11 18 = 12 19 = 13 |
20 = 14 21 = 15 22 = 16 23 = 17 24 = 18 25 = 19 26 = 1A 27 = 1B 28 = 1C 29 = 1D 30 = 1E 31 = 1F 32 = 20 33 = 21 34 = 22 35 = 23 36 = 24 37 = 25 38 = 26 39 = 27 |
40 = 28 41 = 29 42 = 2A 43 = 2B 44 = 2C 45 = 2D 46 = 2E 47 = 2F 48 = 30 49 = 31 50 = 32 51 = 33 52 = 34 53 = 35 54 = 36 55 = 37 56 = 38 57 = 39 58 = 3A 59 = 3B |
60 = 3C 61 = 3D 62 = 3E 63 = 3F 64 = 40 65 = 41 66 = 42 67 = 43 68 = 44 69 = 45 70 = 46 71 = 47 72 = 48 73 = 49 74 = 4A 75 = 4B 76 = 4C 77 = 4D 78 = 4E 79 = 4F |
80 = 50 81 = 51 82 = 52 83 = 53 84 = 54 85 = 55 86 = 56 87 = 57 88 = 58 89 = 59 90 = 5A 91 = 5B 92 = 5C 93 = 5D 94 = 5E 95 = 5F 96 = 60 97 = 61 98 = 62 99 = 63 |
100 = 64 101 = 65 102 = 66 103 = 67 104 = 68 105 = 69 106 = 6A 107 = 6B 108 = 6C 109 = 6D 110 = 6E 111 = 6F 112 = 70 113 = 71 114 = 72 115 = 73 116 = 74 117 = 75 118 = 76 119 = 77 |
120 = 78 121 = 79 122 = 7A 123 = 7B 124 = 7C 125 = 7D 126 = 7E 127 = 7F 128 = 80 129 = 81 130 = 82 131 = 83 132 = 84 133 = 85 134 = 86 135 = 87 136 = 88 137 = 89 138 = 8A 139 = 8B 140 = 8C 141 = 8D 142 = 8E |
143 = 8F 144 = 90 145 = 91 146 = 92 147 = 93 148 = 94 149 = 95 150 = 96 151 = 97 152 = 98 153 = 99 154 = 9A 155 = 9B 156 = 9C 157 = 9D 158 = 9E 159 = 9F 160 = A0 161 = A1 162 = A2 163 = A3 164 = A4 165 = A5 |
166 = A6 167 = A7 168 = A8 169 = A9 170 = AA 171 = AB 172 = AC 173 = AD 174 = AE 175 = AF 176 = B0 177 = B1 178 = B2 179 = B3 180 = B4 181 = B5 182 = B6 183 = B7 184 = B8 185 = B9 186 = BA 187 = BB 188 = BC |
189 = BD 190 = BE 191 = BF 192 = C0 193 = C1 194 = C2 195 = C3 196 = C4 198 = C6 199 = C7 200 = C8 201 = C9 202 = CA 203 = CB 204 = CC 205 = CD 206 = CE 207 = CF 208 = D0 209 = D1 210 = D2 211 = D3 212 = D4 |
213 = D5 214 = D6 215 = D7 216 = D8 217 = D9 218 = DA 219 = DB 220 = DC 221 = DD 222 = DE 223 = DF 224 = E0 225 = E1 226 = E2 227 = E3 228 = E4 229 = E5 230 = E6 231 = E7 232 = E8 233 = E9 234 = EA 235 = EB |
236 = EC 237 = ED 238 = EE 239 = EF 240 = F0 241 = F1 242 = F2 243 = F3 244 = F4 245 = F5 246 = F6 247 = F7 248 = F8 249 = F9 250 = FA 251 = FB 252 = FC 253 = FD 254 = FE 255 = FF |
16.1.3. Hexadecimal Values for Web Palette Colors
The web palette is a set of 216 colors that will not shift or dither when rendered in browsers on 8-bit monitors (for a thorough explanation of the web palette, see Chapter 3, "Web Design Principles for Print Designers"). All colors in the web palette are made up of combinations of the following six hexadecimal values: 00, 33, 66, 99, CC, and FF.
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| 15.7. Demystifying CGI |  | 16.2. Specifying Colors by Name |
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