Looks mostly to be the choices for the rgb triplets aren't very distinctive, but a contributing factor is there just aren't many pixels set.
You don't need anything fancy to set bold font, just modify the Label function:
Label = @(ii,s) sprintf('\\color[rgb]{%0.3f, %0.3f, %0.3f}\\bf%s', C(ii,:), s);
This is all standard TeX, w/ the TextInterpreter stuff you needs must escape any LaTeX with $$ and, of course, when you turn it on, all the standard TeX stuff goes south. You can't mix the two...
Best Answer