Here's the full list:

aliceblue, antiquewhite, aquamarine, azure, beige, bisque, black, blanchedalmond, blue, blueviolet , brown, burlywood, cadetblue, chartreuse, chocolate, coral, cornsilk, crimson, cyan, darkblue, darkcyan, darkgoldenrod, darkgray, darkgreen, darkkhaki, darkmagenta, darkolivegreen, darkorange, darkorchid, darkred, darksalmon, darkseagreen, darkslateblue, darkslategray, darkturquoise, darkviolet, deeppink, deepskyblue, dimgray, dodgerblue, firebrick, floralwhite, forestgreen, gainsboro, ghostwhite, gold, goldenrod, gray, green, greenyellow, honeydew, hotpink, indianred, indigo, ivory, khaki, lavender, lavenderblush, lawngreen, lemonchiffon, lightblue, lightcoral, lightgoldenrodyellow, lightgreen, lightgrey, lightpink, lightsalmon, lightseagreen, lightskyblue, lightslategray, lightsteelblue, lightyellow, lime, limegreen, linen, magenta, maroon, mediumaquamarine, mediumblue, mediumorchid, mediumpurple, mediumseagreen, mediumslateblue, mediumspringgreen, mediumturquoise, mediumvioletred, midnightblue, mintcream, mistyrose, moccasin, navajowhite, navy, oldlace, olive, olivedrab, orange, orangered, palegoldenrod, palegreen, paleturquoise, palevioletred, papayawhip, peachpuff, peru, pink, plum, powderblue, purple, red, rosybrown, royalblue, saddlebrown, salmon, sandybrown, seagreen, seashell, sienna, silver, skyblue, slateblue, slategray, snow, springgreen, steelblue, tan, teal, thistle, tomato, turquoise, violet, wheat, white, whitesmoke, yellow, yellowgreen



Update:

now also supporting system colours, per Calm_Pear's request:

ActiveBorder, ActiveCaption, AppWorkspace, Background, ButtonFace, ButtonHighlight, ButtonShadow, ButtonText, CaptionText, GrayText, Highlight, HighlightText, InactiveBorder, InactiveCaption, InactiveCaptionText, InfoBackground, InfoText, Menu, MenuText, Scrollbar, ThreeDDarkShadow, ThreeDFace, ThreeDHighlight, ThreeDLightShadow, ThreeDShadow, Window, WindowFrame, WindowText