I was surprised to find a huge listing of pre-defined colors which can be used as parameters with HTML Tags. Custom colors are defined in hex as in #RGB. But have a look at the pre-defined... (pretty kewl names huh?) colors and if you dont have a color which you are looking for, by all means RGB... so here goes. The names given below are the predefined names themselves in their own color!
Oh! I forgot...BLACK 'cause it aint show up in the default backgound! Block the empty space below AQUA to see it.

AQUA

BLACK

BLUE

BLUEVIOLET

BROWN

BURLYWOOD

CADETBLUE

CHOCOLATE

CORAL

CORNFLOWERBLUE

CRIMSON

CYAN

DARKBLUE

DARKCYAN

DARKGOLDENROD

DARKGRAY

DARKKHAKI

DARKMAGENTA

DARKOLIVEGREEN

DARKORANGE

DARKORCHID

DARKRED

DARKSALMON

DARKSEAGREEN

DARKSLATEBLUE

DARKSLATEGRAY

DARKTURQUOISE

DARKVIOLET

DEEPPINK

DEEPSKYBLUE

DIMGRAY

DODGERBLUE

FIREBRICK

FORESTGREEN

FUCHSIA

GOLD

GOLDENROD

GRAY

GREEN

HOTPINK

INDIANRED

INDIGO

KHAKI

LIGHTCORAL

LIGHTSALMON

LIGHTSEAGREEN

LIGHTSKYBLUE

LIME

LIMEGREEN

MAGENTA

MAROON

MEDIUMAQUAMARINE

MEDIUMORCHID

MEDIUMPURPLE

MEDIUMSEAGREEN

MEDIUMSLATEBLUE

MEDIUMTURQUOISE

MEDIUMVIOLETRED

MIDNIGHTBLUE

NAVY

OLIVE

OLIVEDRAB

ORANGE

ORANGERED

ORCHID

PALEVIOLETRED

PERU

PLUM

PURPLE

RED

ROSYBROWN

ROYALBLUE

SADDLEBROWN

SALMON

SANDYBROWN

SEAGREEN

SIENNA

SILVER

SKYBLUE

SLATEBLUE

SPRINGGREEN

STEELBLUE

TAN

TEAL

TOMATO

TURQUOISE

VIOLET

WHITE

YELLOW

YELLOWGREEN

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Maintained by Prakash Raman