PLEASE READ carefully my previous post.
Indeed the colors go like this (Use Gimp or Photoshop or PaintShopPro or whatever you like but DO IT).
R,G,B:
60,60,60
60,60,60
… wide section with same flat color …
60,60,60
59,59,59
59,59,59
… wide section with same flat color …
59,59,59
58,58,58
… wide section with same flat color …
58,58,58
58,58,58
etc.
YOU CAN NOT HAVE MORE COLOR PRECISION.
So if you see the lines separating the uniform parts it means that a) you have very good eyes and/or b) the gamma/brightness/contrast of your monitor is set too high.
With high range, it is normal that those lines disappear, because color changes almost every line.
Don’t rely on floating point measures of color. Stay with 8bit per color component, it means GLubyte, integer values ranging from [0 to 255].
Really, try the solution I gave, that is do not use plain gray, but slightly modified colors like glColor3ub (74 , 76 , 75 );