what RGB is blue?

[Tiemo Hollmann TB]

Hello,

I am taking the mousecolor at different points from an image by script (not
by clicking). I would like to analyse if the color I've taken is a "kind of
blue", or another color. I want to change the backgroundcolor of an image.
The background is always blue, but different blues and changing over the
background. So what I want to do is to verify, what is background and what
is foreground of my image.

100% pure blue would be 0,0,255. But for a human being 25,75,130 (greyblue)
is also still blue, but 240,20,180 is pink, though the third RGB value is
higher as in my greyblue.

So I can't just check only the third RGB value, neither the sum or cross
total. Has anybody ever heard, if you can define at all by math "what is
blue"?

Any color specialist around here?

Tiemo