Really you could make it better without a "colourblind mode" - by getting a colourblind person to have a look at it (as we used to do, when designing web pages) - they're easy to find (10% of males have defective colour vision to some extent - it's very common). The two most common versions are red/green and blue/yellow. This does NOT mean that, for instance, a red/green colourblind person cannot tell red from green - red will be much less bright (so purple will look like a deep blue) and green is (normally) completely shot (so a light green probably looks like yellow - a deep green could be orange).
The upshot is that thing would be massively improved if they didn't expect people to tell blue from purple or yellow from green.
