Hello, I’m a real beginner, so forgive me if I’m asking for something obvious 
I have a problem with bevel and subdivision surface modifiers. After I apply them to the object, the colours of some faces start to ‘melt’ together in a bit weird, unexpected way. Do you know what might be the problem, and how can I solve it? If I extend the nuber of subdivisions, the colours mix in more regular, but still unexpected way. Here are the pictures of the problem.
I take it that you have object with two colors assigned to it right? That wavy pattern at top surface comes from triangular meshes you have there. Make it a quad and problem will go away.