I wouldn't disagree with any of that per se, but, of course, screen casting is, I suspect, far less bothered about the condition of the headshot, anyway, as what they are most interested in seeing for specific purposes these days is showreel material or uploads, except perhaps when it comes to commercials casting. It is interesting to compare UK and US standards in photography - and, while it has to be said that a lot of the basic physical characteristics are revealed a lot more accurately in colour than in black and white (for instance, hair and eye colour), there is certainly a tendency for US style to glamourise, because that is the standard to which the US marketplace aspires - I have honestly never seen a US shot in which the actor did not look as beautiful or handsome as it was possible to make them look (yes, even the old, fat, wrinkled character actors look stern or charming or apple-cheeked or grandfatherly, according to taste) - and while the quality of the lighting and reproduction seems to me second to none, I suspect the UK system still distusts this aesthetic, because, deep down, it is a not a marketplace that is geared towards glamourising things (though it has become ever more US like in recent years). For all that, though, I would certainly not think that a colour headshot would be considered inappropriate by any modern thinking casting director! I'm just not sure it would prove any more effective than a black and white shot when the market is still geared so traditionally towards seeing black and white as standard.