Some years ago, when computers supported max 256 different colors, a list of 216 "Web Safe Colors" was suggested as a Web standard, reserving 40 fixed system colors.
The 216 cross-browser color palette was created to ensure that all computers would display the colors correctly when running a 256 color palette.
This is not important today, since most computers can display millions of different colors. Anyway, here is the list:
| 000000 | 000033 | 000066 | 000099 | 0000CC | 0000FF |
| 003300 | 003333 | 003366 | 003399 | 0033CC | 0033FF |
| 006600 | 006633 | 006666 | 006699 | 0066CC | 0066FF |
| 009900 | 009933 | 009966 | 009999 | 0099CC | 0099FF |
| 00CC00 | 00CC33 | 00CC66 | 00CC99 | 00CCCC | 00CCFF |
| 00FF00 | 00FF33 | 00FF66 | 00FF99 | 00FFCC | 00FFFF |
| 330000 | 330033 | 330066 | 330099 | 3300CC | 3300FF |
| 333300 | 333333 | 333366 | 333399 | 3333CC | 3333FF |
| 336600 | 336633 | 336666 | 336699 | 3366CC | 3366FF |
| 339900 | 339933 | 339966 | 339999 | 3399CC | 3399FF |
| 33CC00 | 33CC33 | 33CC66 | 33CC99 | 33CCCC | 33CCFF |
| 33FF00 | 33FF33 | 33FF66 | 33FF99 | 33FFCC | 33FFFF |
| 660000 | 660033 | 660066 | 660099 | 6600CC | 6600FF |
| 663300 | 663333 | 663366 | 663399 | 6633CC | 6633FF |
| 666600 | 666633 | 666666 | 666699 | 6666CC | 6666FF |
| 669900 | 669933 | 669966 | 669999 | 6699CC | 6699FF |
| 66CC00 | 66CC33 | 66CC66 | 66CC99 | 66CCCC | 66CCFF |
| 66FF00 | 66FF33 | 66FF66 | 66FF99 | 66FFCC | 66FFFF |
| 990000 | 990033 | 990066 | 990099 | 9900CC | 9900FF |
| 993300 | 993333 | 993366 | 993399 | 9933CC | 9933FF |
| 996600 | 996633 | 996666 | 996699 | 9966CC | 9966FF |
| 999900 | 999933 | 999966 | 999999 | 9999CC | 9999FF |
| 99CC00 | 99CC33 | 99CC66 | 99CC99 | 99CCCC | 99CCFF |
| 99FF00 | 99FF33 | 99FF66 | 99FF99 | 99FFCC | 99FFFF |
| CC0000 | CC0033 | CC0066 | CC0099 | CC00CC | CC00FF |
| CC3300 | CC3333 | CC3366 | CC3399 | CC33CC | CC33FF |
| CC6600 | CC6633 | CC6666 | CC6699 | CC66CC | CC66FF |
| CC9900 | CC9933 | CC9966 | CC9999 | CC99CC | CC99FF |
| CCCC00 | CCCC33 | CCCC66 | CCCC99 | CCCCCC | CCCCFF |
| CCFF00 | CCFF33 | CCFF66 | CCFF99 | CCFFCC | CCFFFF |
| FF0000 | FF0033 | FF0066 | FF0099 | FF00CC | FF00FF |
| FF3300 | FF3333 | FF3366 | FF3399 | FF33CC | FF33FF |
| FF6600 | FF6633 | FF6666 | FF6699 | FF66CC | FF66FF |
| FF9900 | FF9933 | FF9966 | FF9999 | FF99CC | FF99FF |
| FFCC00 | FFCC33 | FFCC66 | FFCC99 | FFCCCC | FFCCFF |
| FFFF00 | FFFF33 | FFFF66 | FFFF99 | FFFFCC | FFFFFF |
