Second question first.
A laser is “tuned” to a certain light wave frequency that is absorbed by the ink. Hi-intensity, focused laser breaks up the ink. Your body eventually absorbs the ink.

The Sun is very broad spectrum of light, and other radiant energy. In fact our “visible” light is only a small portion of the total radiant energy – think UVA, UVB, infra-red, etc.

Over decades sun exposure will fade some inks more than others but a magnifying glass is NOT the way to go!

first question second.
A lot depends on how “mixed” the inks are. Remember the laser is “tuned” for a specific color, since black absorbs all wavelengths of visible light the black ink absorbs the most energy. It would not surprise me if black could be “lasered” and the other colors would simply fade some. On the other hand, if inks are mixed really well, the black’s absorbtion could, maybe drastically effect the other colors.

(Nothing like a not sure, heh?)