understanding rgb:a0/a0/a0 color code format

Johnny <[email protected]>
Newsgroups gmane.comp.window-managers.icewm.user
Message-ID <[email protected]>
Hi
I am trying to understand how to find the color code format for rgb:a0/a0/a0
I have seen this in flubox themes and others, I know that #000000 is black
I have the color2, xcolmix, xcolorsel installed

I have googled and found rgb:255,255,255 but I am not finding 
rgb:a0/a0/a0 color code format
I am using Debian lenny

Where can I find info on how to understand this color code format

Johnny

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