黑色(hēi sè) - black, the colour black in Mandarin

黑色 (hēi sè) is the noun for the colour black. Mandarin builds most colour names this way: a colour character plus 色, giving 红色 (red), 蓝色 (blue), 白色 (white). Use 黑色 when you are naming the colour itself, as in 我喜欢黑色.

Before a noun you need 的: 黑色的外套, 黑色的头发. In the predicate you say 是黑色的, not just 是黑色 on its own. That 的 is doing real work, and dropping it sounds clipped.

The trap for English speakers is that 黑 also exists on its own, and the two are not interchangeable. Bare 黑 is the adjective and takes 很 like any other stative verb: 天很黑 means it is very dark, not it is very black. 黑色 is a thing you can point at; 黑 is a quality something has. Use 黑色 for the colour, 黑 for darkness.