The question is: there's a shader, it has one main solid color that is to be mixed with another. That “another” color should be a random one, but taken from a certain color range, for example, from 128, 15, 36 - 128, 15, 56.
Mix these two border colors with mix Color VOP using random number as a bias value.
Remember that you have also HSV_to_RGB and RGB_to_HSV VOPs, so you can control only hue value of your colors if mixing three rgb channel it's not what you want.