That is not what the Wiki says!On reading the code you will see that the value will be interpreted as a named colour (eg. "gold") if the value contains any characters outside 0-9A-Fa-f. That's exactly what's going to happen if you include a # prefix. Therefore catavolt's advice to not include the prefix is good.
The Wiki implies that either decimal or hexadecimal values can be specified (and gives an example). A value containing one or more hexadecimal digits is clearly hex (if it is valid). But if a value contains only decimal digits (e.g. 12345678), how does the skin engine know whether the value is decimal or hex? I imagined that that was what the "#" prefix is for:
12345678 -- a decimal number
#12345678 -- a hexadecimal number
Also, I have just tried both "cc00ff00" and "#cc00ff00" (without the quotes), and both give the same result -- a light green background.
-- from CyberSimian in the UK