I suggest you keep it simple, i.e. only two
colours if possible, but
make them configurable for the benefit of those with visual disabilities.
Andrew Bryant
I wondered about that part too, especially about color blind people.
I don't know any, as far as I know, and so I have no experience with it.
So just maybe a greyscale mode would help? This would depend heavily on
the background color though. So maybe Arnolds idea with the background
color on the lower end makes sense. You still need to see that there is
something that shows you something and you still need a certain
color/intensity range, or it's rather useless.
In greyscale white background to black for highest intensity would offer
the largest range. I guess some light grey to black would still be good
enough.