The difficulty seeing “blue” is progressive. An average 75 year old will see a certain darkish blue significantly harder than an average 60 year old. Also, depending on many variables, a 50 year old may not see the same hue properly as well. It is not simply calendar age.
I believe, an ability to adjust luminosity of the histogram colors “for all users” will be the best option. (Of course, I have no idea about the feasibility of this). Most people will never touch the red, few would play with the green and a great many -on one day or another- will adjust the blue.