Hi, I'm new around here, but I thought I'd start by replying to something that I know a little about. I'm a Chicana living in LA and when I saw the topic for the thread I wanted to see what it was all about.
First off, there were African slaves in Mexico. If you traveled to Veracruz in Eastern Mexico (by the gulf) you'd notice that there are some darker skinned people there. There have also been lots of influences in things like music. In the colonial caste system Africans were at the bottom of the social ladder. Of course, the Spanish "peninsulares" were at the top. The natives were also at the bottom. Basically, the darker your skin, the lower you were in society. Its even that way today in other Latin American countries too, just check out soap operas (or telenovelas) on Spanish language television. The lead roles are usually played by European-looking men and women. Sometimes Africans and Indians are villfied too. Racism and classism play a big role in Latin American society.
I forgot who mentioned something about having to speak Spanish to be accepted. That's true, but I don't know about being "brown enough." Most of the time for women light skin is better than dark skin. IMHO light skin is still valued more than darker skin. Its easy to see when people gush over fair-skinned babies with light hair, and they ignore the "prieto" (darker one).
In terms of interaction between both groups, I don't know much. I'm in college and I work with a Chicana/o student group. We often work with the African Student Union on all sorts of issue. The constant propositions are often targeted at youth of color so we collaborate on things like bringing back affirmative action and opposing certain state initiatives (props 21, 209...). I don't know why we fight over the crumbs.