keep it out of the sun- wash in cold water with gentle detergent-
just like all fabrics---not all blacks are created the same-
i have had good luck with Kona Black; Benartex has a nice stable true dark black- the thin- already kind of lighter color blacks found at places like Joanne's tend to fade the fastest...and you never know what color they will fade to- some turn brown, some a shade of gray...some more reddish- depends on the (formula) used to achieve the black in the first place
but sunlight, warm/hot water & strong detergent will all fade blacks- and other dark colors