"Readable" is a somewhat subjective measure, dependent on things like monitor settings, gender (most colour deficiency is in Males) and age (the amount of light going through the cornea of a 60 year old is under 25% of what used to go through at age 18).

You could take a slightly "brute force" approach by preserving the hue, forcing saturation to 1.0 and brightness to 0.5.