It's not that black dancers on Strictly are being directly rejected by the public - we vote to save, not vote to evict - it's just that they seem to have more of a battle to gain people's support. It's more of an unconscious racial bias that most people are unaware of, rather than the Great British Public actively rooting against minority contestants, which is what most people on this thread seem to think is going on.
And even though yes, a lot of minority contestants have done well on this show, they still make up a disproportionate amount of bottom two serial survivors (meaning those who have survived at least two bottom twos) (off the top of my head - John Barnes, Simon Webbe, Heather Small, Denise Lewis, Patrick Robinson, Sunetra Sarker, Ricky Whittle, Michelle Williams, Audley Harrison, now Jamelia - now compare that to the overall amount of people who survive multiple bottom twos and it won't be the same ratio as the ratio of races in the competition) and shock exits (DJ Spoony, Ray Fearon, Jimi Mistry - all three had high average scores and yet none of them made it past ninth place).
Another thing: Denise Lewis and Natalie Gumede both did full leaderboard plunges from the top into the bottom two in their respective semi-finals (and I suspect the bottom-two bounce helped propel both of them past a last-place finish in the final), so I don't think we can say 'Denise only lost because of Jill's jive'.