Simple disguise is generally the norm in ceremonial customs of this sort. In Europe, it is most convenient to use soot to blacken the face; in Africa, ash is used to whiten it. There is no racist motive inherent in either action. In the same way, jackets were traditionally worn inside-out; the point is to reverse the normal appearance along with a concomitant reversal of normal behaviours. More complex forms of disguise are also used (the "Burry Man" has close analogues in Eastern Europe and in Africa, for example) but simple face-changing is a base-line and universal behaviour.

Looked at out of its historical context, it is certainly true that a racist sub-text might be imagined by an observer ignorant of the way such things work, and who does not understand that Western Europe, just as much as other parts of the world, possesses a range of quite innocent traditional practices capable of extensive mis-interpretation if approached judgementally and without empathy or the will to understand.

It is an issue that needs to be addressed carefully in order to avoid misunderstanding and injured feelings, but I'd think that the way forward would be to point to the close parallels in other cultures by way of analogy and explanation rather than simply to panic in the face of the knee-jerk attacks that seem to come mostly, not from the Black British (who are not idiots) but from "right-on" middle-class Whites: who, all too often, are idiots; and bigots, come to that, though it's an odd and perverse bigotry that isn't susceptible to reason.

See also -for example- various discussions here in which people have agonised about such foolishness as whether Lord Thomas and Fair Eleanor (which features a "brown girl") is "racist". They have been, as here, through ignorance, imposing a modern, anachronistic and irrelevant sensibility upon a completely unrelated situation.

With McGrath, I initially though that this discussion might be more appropriate "above the line", given that thread headings like "tech" and "folklore" are continually abused here to give undeserved prominence to irrelevant rubbish; having read some of the later contributions to it, though, I think that perhaps it should stay here after all.