That heavily depends on the era you have in mind. In the 19th century and until WW I it usually was a combination of red and blue.
blue because they liked it
It was said that they wore mainly Blue until WW2.
they just wore whatever they had. but they were issued armor for the head,chest, and biceps.
The kit is blue jersey, white shorts and red socks, recalling the colors of the french flag.
The uniforms in the French military are resembling those of western countries: combat boots, camouflage fatigues, beret or forage cap depending of the units.
A zouave is one of an active body of soldiers in the French service, otherwise known as Kabyle, but now those who wear the Kabyle dress.
No, Mexicans don't HAVE to wear bright colors.
Probably not any more than Americans, as they both share the same colors on their flags.
you wear dark colors
they wear red...
I know that the French soldiers wore a uniform similar to the chasseurs, which were painted in this painting http://commons.wikimedia.org/wiki/Image:Napoleon_Guard_Chasseurs_by_Bellange.jpg but I am not exactly sure what the Mexicans wore, though I have read that it was black
i think they wear boots