In certain contexts the "geniuses are wacky - and quite possibly cnuts" trope is, seemingly, colour blind:
Take - say - Miles Davis. Or Muhammad Ali. Everyone loves 'em. In spite of the fact that they were clearly "difficult" (or even a bit cnutish, depending on who you believe).
But they were a) a jazz musician and b) a boxer. A non-white person might be "accepted" (to use your aptly highlighted term) when he (makes it even easier if "he" is a "he", of course) appears as something...suitable: a black man being either a jazz musician or a boxer is hardly controversial (it's the opposite, in fact, and only confirms the status quo as such). There are numerous other examples from contexts where "wackiness and/or cuntishness" would not disqualify a non-white person from "genius" status (to some degree or other).
Presently, though, a wacky - and potentially cnutish (in one way or another) - black football manager (or bank manager, or prime minister in a non-African country) would be a different kettle altogether.
Or? Would it - really?
Yes, of course it would. And that's the problem. We are nowhere near a point where it would not be a different kettle.
Granted, it's an entire world of clichéd thinking (something endemic in football). The trouble is, I think, that assumptions about Black people - and Black athletes in particular - are so ingrained that even our praise and admiration is tainted by received 'wisdom', these assumptions. And that's before we even start discussing individual, varying personalities. In a sense, analysis is a form of control. For example, this photo of the boxing champion Sonny Liston was featured in an excellent biography of Ali:
According to the esteemed biographer, this 'soulful' photograph tells an entire history - not just Liston's personal story, but a history of his race. Sonny's trials and triumphs don't, apparently, merit the kind of flattering storifying that white heroes traditionally enjoy (the kind which hints that white heroes are basically gods, even if flawed gods). This crude, snapshot treatment and subsequent transformation of Sonny's life makes him an emblem rather than a person. As tempting as it undoubtedly is to more or less concur with the well-intended and apparently guileless author, his depiction is sheer Romance. It
categorises Sonny, makes him akin to a fictional character - he is now a narrative we can mould to our liking and approval - rather than a living being of nuance like the rest of us (white people). This literary portrayal, as it over-reaches for empathy, is nonetheless backhanded praise. In the safe and sanctioned hands of an artificer, it turns an individual into an artefact. Worse, it's in the shabby tradition of the 'noble savage' which essentially is a particular kind of white mans' late-in-the-day regret over murder and pillage; the irony of great Black boxers being forced or remunerated victors and victims fighting before white eyes has been artfully dismissed from the discussion. Even our praise shames us, even our acceptance is loaded...
In the eyes of the wider public anyway.