Is there any specific measure of how the color of a surface affects the surface's reflectivity?

Question

For example, a yellow colored block reflects more light than a blue colored block. Is there any rule of thumb, or formula or something, that could give me a fraction of some sort describing how a one color reflects more or less than another?

Answer 1

Benjamin Moore records the reflectivity of their paints. (Other brands probably do as well. Sometimes this is an issue for commercial buildings, the architect or lighting designer will specify a paint with X amount of light reflectivity.)
So if you could match a paint to something you want to know the reflectivity of, the index would give you the reflectivity.
For a formula, you could contact the web site of one of the paint companies and ask.

Answer 2

I dont have any formulas or fractions for you but I do have some other info that might be usefull. When you are looking at colors what you see is the reflected light comming off of that object. A yellow colored block does not reflect more light, but rather reflects a more intense color to our eyes. Under white light the blue block will reflect just as much but will not be as intense to our eyes. Under white light all colors will reflect equally. It all has to do with the electromagnetic spectrum. White light is the combonation of all colors in the spectrum. If you were to shine a blue spot light on the yellow and blue blocks. The yellow block would no longer be yellow, it would be a very dark, almost black color there would be no yellow light for the yellow pigment to reflect. The blue block would be blue because the blue pigment would have pleanty of blue light to reflect. Hopefully this kind of answers your question.