Fernando, What you have written is the truth! I have seen it happen several times. Here is a personal example:
Even though I have dated a Black Lady, then dated a Mulatto Lady who had Mulatto Children, have been intimate with people of many different skin tones, have donated to the NAACP and other Orgs, have been sponsoring children through Children International for 10 years-(None of whom were/are White), live in a neighborhood that is only 7% White, have advocated and sent letters approving of Herman Cain as President, been in business with a Black Lady and a Lady from Mexico, have signed several petitions against racial injustices, etc. I have still been accused by a few people of being racist (IN NO WAY am I mentioning any people in particular on this or any other website). When I have looked back, I have noticed that many of those same people who have done the accusing are having issues in their own lives, so they project their own insecurities onto others, hoping that all eyes will be taken off of them.
So, in answer to your question, Yes, I have seen it happen, not only to myself, but others. It really sucks to get blamed for something you are not or have not done. I used to let it bother me, but since realizing that the problem often lies with the accusers, I try to take it with a grain of salt, and find myself pitying them instead. Besides that, the people who really know me, know that the accusations are not true anyways, so it really doesn't matter in the grand scheme of things.