charlottebronte... this is your Dales mare? I might have to go and find one of the pics you've posted - but basically a black will have black hair, dark skin, and no paler fawn areas anywhere (like around the eyes, muzzle, flanks and so on). AH Mahal is a true black - note on his pics how his muzzle is black too, and he has no lighter areas at all. Virtuallyhorses' Imp, however, is brown - he has the same black or near black colouring on his body, but paler brown colouring at muzzle and so on. That's a brown horse - research suggests that brown (or seal) horses may well be bay with some kind of modifier, possible sooty. One school of thought says that the only difference between a mahogany bay and brown is the degree to which the darker hair is spread over the body.
So... if she has brown anywhere, she's not black - she's either seal brown or dark bay. Lots of blacks do fade in sunlight, so that's not really an indication (there is a form of black known as non-fading black, or true black - but it's not that common) but the key question is whether she has lighter points.