As long as the spectral sensitivity of the meter and the film are a decent match then the colour doesn't matter. You're just choosing an intensity. If on the other hand you metered a red area while shooting ortho film (that can't see red!) then that region is going to come out a lot darker than you'd hoped for.

If you place two colours (in separate exposures) on the same zone, they will end up the same shade of grey in the prints. If they're in the same scene/exposure and one is darker than the other, then obviously you can't place them on the same zone unless you start filtering the light.

If you have yellow and purple areas that meter identically and you want the yellow to look brighter, you could use a yellow or orange filter on the lens to reduce the brightness of the purple area. You would need to meter each area through the filter to observe the exact effect that the filter has on each colour.