The Gimp (which I think you are using) does have attempts at color-blind perceptual models.

View -> Display Filters -> Color Deficient Vision

You can select between
Tritanopia
Deuteranopia and
Protanopia

(yes, I know I wrote them 3,2,1)

I don't know how good they are, as I'm not one of the 10%

Unfortunately, it's not as simple as that. The phrase "red-green" covers a wide variety of colour blindness types, and doesn't describe the situation very well.

There are four common types of colour blindness: Protanopia (no red detectors), protanomaly (red detectors are green-shifted, deuteranopia (no green detectors) and deuteranomaly (green detectors are red-shifted). All four of these are included in the phrase "red-green".

In all of these types, the normal 3-dimensional colour space is compressed to a 2-dimensional one (or a 2.5-dimensional one, with reduced resolution in the third dimension). This means that in a Hue-Saturation plot, there is a direction such that all colours in a line parallel to this direction look identical.

Personally, I have protanopia (no red cones at all, with a corresponding increase in the number of green cones). Roughly speaking, my "neutral curve" runs parallel to the red -> cyan axis (through grey).

If you look at the web-safe colour palette at http://www.visibone.com/colorlab/big.html
then, to me all the cyans appear to be grey.
CFF, 9FF, 6FF, 3FF and 0FF all look nearly the same
699, 399 and 099 all look the nearly the same as 999 (a grey)
Likewise the "pure" yellow (FF0) is very close to the "pure" green (0F0) [though it's worth pointing out that RGB uses a very "bright" green, I don't normally have difficulties between greens and yellows] and similarly the blues look very identical to the magentas.

In fact, I don't have a sense of "purple" at all, making telling blue from purple very difficult. This makes sense if you imagine that the brain defines the colours as
Blue = Blue detector & Green > Red
Purple = Blue detected & Red > Green
Since I don't detect red, I can't distinguish the two...

For my type of colour blindness, the most common problems are
Dark Green & Brown
Blue & Purple
Grass Green & Orange

People with deuteran tendancy (no green detectors), have a completely different neutral curve, so will confuse a different set of colours...

And, just to complicate matters, protans like myself see red as being a lot darker, so can't read black on red (or red on black).

Thanks, that ought to be usefull. In my latest proposal I can tell the difference in all three cases, so assuming it's not to boken it'll do.

Paul: Thank you for your thoughly eplanation. I thought red-green color blindnes just was thet red and green sensors gave the same output, thanks for correctling my error.

I'll try to remember to run all my future proposals through grayscale and Color Deficient Vision filters, though I'll not be as concerned with astetical properties when doing so.

Best Regards
- Jonno

There's an online tool at http://www.etre.com/tools/colourcheck/ that checkes the "colour distance" between two colours. (It's intended for checking for suitability between text / background colours, but I don't see why we can't use it to assess the difference between colours in our counters)