Do not know that there is any sort of rule but usually the section under the chair rail would be darker as if to have some substance on which something above it could rest. If you make it lighter and put a heavy color on top it can look like it is floating and on something not solid enough to hold it. Some elegant papers might look nice in your situation if you have the budget.
Now I lost you at one point. Are you trying to just use 1/4 round between the wall and floor. I think this could look rather anemic without some sort of baseboard. I would lean toward painting all the trim the same color. Or leave it all natural wood finished.
Now I lost you at one point. Are you trying to just use 1/4 round between the wall and floor. I think this could look rather anemic without some sort of baseboard. I would lean toward painting all the trim the same color. Or leave it all natural wood finished.