Black Canvases

It wouldn't be a Bob Ross canvas, would it? He popularized canvases covered with a black "gesso", on which he would then paint with something he called "liquid clear", into which he would then work; or he would paint colours over the black, and then pick them up with an application of his "liquid white". Quite why he found this helpful in any way is something of a mystery to me, but if you pursue Bob Ross demonstrations on YouTube, you'll find him employing them now and then. He used modified oil paints, of course. In your place I should be inclined to paint a few coats of white over the black and treat it as a normal canvas - it offers very few if any advantages in acrylic painting (that you couldn't achieve with an ordinary canvas if you just brushed black onto it yourself in pursuit of various techniques) and I think it was a bit of a gimmick, frankly. Obviously, it will be as sound as any other canvas to work with - but you asked what the purpose or advantage was, and having watched a fair number of BR video demos (largely because his voice sends me to sleep) I've never understood what could be achieved with a black canvas that couldn't (and better) be achieved with a conventional one.

I can't see any benefits in painting on a black ground. Unless the paint is spread on with a trowel, the black will be visible in parts and the picture will look gloomy. Might be good if you're a Goth though. Warm biscuit coloured grounds are useful especially when painting landscapes. You can leave bits of the undercoat showing and it seems to make the painting more interesting.

As someone who spreads paint on with a trowel (aka painting knife) ... and who leaves unpainted areas of natural linen ... and who likes drawing on black paper... you'd think I might have a use for a black canvas. But I've seen them on sale at Great Art and I didn't find it very hard to ignore them. If I did happe to have one, I think I'd use acrylics on it, and go for a very bright, false colour, image with a knife.