Nairo Quintana has spoken candidly about racism in the pro peloton.
It's also been noted that Quintana gets plenty of racism from other Colombians - for being indigenous. I've also seen some rather dubious comments about his looks on this forum, that show a basic lack of knowledge about indigenous peoples of the Americas and what they normally look like.
Of course, as I said a long time ago on that other thread, there is a big distinction between socio-economic explanations (largely to do with poverty and opportunity) and racial-physiological explanations (people X are naturally better at A or B than people Y). That's not to say that all physiological explanations are rubbish: the particular story of slavery and survival
might have created conditions for a kind of selectivity as the program mentioned above explored. But it should be noted that this does not mean 'black people' are naturally of a certain fixed physical type - quite the opposite, in fact.
Pro-cycling developed from Europe, and is still dominated by white Europeans. Some of this is the result of history, some the result of the financial requirements of professional sport and cycling in particular. One thing that is absolutely certain is that it is nothing to do with 'natural' physiological differences - because 'white' is not an physiological cateory with any meaning, any more than 'black' is. However it is certainly a very real one in socio-economic terms.
What I am interested in is the encouragement of cycling in as wide a range of people as possible, and providing opportunities and support to those who would not otherwise get a chance to reach their sporting potential. Sub-Saharan Africa is one of the major potential pools of talent, and there is enormous enthusiasm for cycling in several countries, but it just needs the support and funding. The UCI has been doing a few things, team MTN-Qhubeka is a vital recent step forward, but much more needs to be done. China, also mentioned above, doesn't really need the help - they have both the population and the money should they wish to develop cycling more (and they are doing so on the track and to an increasing extent on the road).