Especially if you can see the numbers embedded in the test image, it's easy to forget that many people can't differentiate red from green, and thus can't see them. But we need to keep that in mind when we are creating data visualizations. (I admit that I sometimes forget.)
Matthias's submission addresses this issue nicely, and provides several alternatives for visualizing data with colors designed to facilitate color differentiation by color-deficient individuals.
So, returning to the "74" image, we might, for instance, revisualize it using an "isolum" colormap:
I reduced the image to four colors before creating this colormap. There are options that I haven't tried yet that may well improve this visualization, but I'll leave that to your exploration.
(Note: I recognize that some say that color deficiency is a boon under some circumstances. Colorblind individuals may, for instance, be better able to see objects that are camouflaged to the rest of us.)
At Matthias's request, I'm including a citation to his publication on the topic:
M. Geissbuehler and T. Lasser "How to display data by color schemes compatible with red-green color perception deficiencies" Opt. Express 21, 9862-9874 (2013)