Dark clothes
It depends on the items. Black cottons likely will eventually turn a shade of grey - or at least a lighter shade of black.
If in doubt, wash the dark clothes with a reduced temperature - say, lukewarm rather than warm, and a reduced quantity of detergent.
I've found over the years, that black dyes and red dyes tend to fade a tad quicker than other colours. Much depends on fabric quality, dye quality, how the item is worn, which detergent is used, whether it is exposed to strong sunlight, whether it is turned inside out on the washing line, etc.
As an example, my dad had a uniformly red shirt which was used for gardening. The back was faded, as it was exposed much more to the sunlight as he was weeding, etc. In comparison, the front of the shirt was a deeper colour, where it was less exposed to the sun.
Another example: I had a pair of black jeans which faded over time - even using liquid detergents. To rejuvenate them, I washed them with Dylon black dye. They looked practically brand new - but the beige label and yellow stitching went black/grey too.