Hi,
From the KML reference
http://code.google.com/apis/kml/documentation/kmlreference.html#color
"Color and opacity (alpha) values are expressed in hexadecimal
notation. The range of values for any one color is 0 to 255 (00 to
ff). For alpha, 00 is fully transparent and ff is fully opaque. The
order of expression is aabbggrr, where aa=alpha (00 to ff); bb=blue
(00 to ff); gg=green (00 to ff); rr=red (00 to ff). For example, if
you want to apply a blue color with 50 percent opacity to an overlay,
you would specify the following: <color>7fff0000</color>, where
alpha=0x7f, blue=0xff, green=0x00, and red=0x00."
Search for HTML Colour Charts which will give you loads of sites
listing various standard/well used codes ... just remember that they
will show them in RGB format so you need to swap them around to BGR
for Google Earth and add the alpha value at the front.
HTML = 123456
GE = aa563412
A colour in KML might look like...
<bgColor>ffd5efff</bgColor>
Hope that helps.
Regards
Nymor