Comment by geon

> it makes no sense to add two RGB colors.

Sure it does. If you work in linear space, the RGB values corresponds to the number of photons.

> It does not make sense to add two RGB colors. The result is not a meaningful physical quantity.

5 photons + 3 photons = 8 photons

> (7.8 earthquake) + (8.3 earthquake) != (16.1 earthequake)

The Richter scale is not linear, so of course it won't work.

More importantly, several earthquakes won't combine onto one. That is not a problem when combining beams of light, since they are already composed of a number of photons each.

Even multiplying RGB values have a physical basis. If one RGB value is the number of photons in a beam of light, the other RGB value represents the probability that the photons will pass through a filter, such as colored glass.