kruler is just what it's name implies; a simple program for measuring between points on the screen. It has nothing to do with what you want.
I've never used kolourpaint or anything similar. In fact, I had to install it just so I could read the manual for you. But it appears that it simply doesn't have the feature you want. I suggest looking around for other image-editing programs.
I generally use the gimp myself. It does have a customizable grid feature, but it's also much heavier and more complex to use than your simple paint programs. I still don't know how to use many of its features myself (and I really wish sometimes that it had simple shape-drawing tools like the paint programs, instead of having to draw and fill selections all the time).