Black
い adjective
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of black? It's also black. Special Note: The noun version of black also exists in Japanese. It is just 黒 with the same pronunciation, but minus the い which makes it adjective-tastic.
くろい
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you: Think of black things. One very common black thing is the common crow (くろ). Associate those two together.
黒いペン、下さい。
A black pen, please.
今夜のパーティーは、黒いドレスで行こうと思う。
I'm thinking of going to the party tonight in a black dress.
ペットの犬の毛が黒いので、うちには白い羊毛のセーターが有りません。
Since our pet dog's fur is black, we do not have any white wool sweaters.