I've also heard this from a few wheel-builders and shop mechanics. Whether they are all indoctrinated by a shared myth is a moot point.
Personally, although I prefer silver spokes, I've never had any trouble with black ones. I build my own wheels though so I make sure the tension is good. Come to mention it I've never had any trouble with the often maligned snow-flaked wheels either...
Anyway, on a two week tour a few years ago one of my mates broke three black spokes in total.
I reckon it was down to his poorly built wheels though, more than the colour of his spokes.