灰 (huī) is an adjective meaning 'grey.' It can describe colors of objects, skies, or moods, and is also used in compound words like 灰色 (huīsè, grey color). On its own, 灰 can also mean 'ash' or 'dust' as a noun.
今天天空灰灰的,好像要下雨了。
Jīntiān tiānkōng huīhuī de, hǎoxiàng yào xià yǔ le.
The sky is gray today; it looks like it's going to rain.
他穿了一件灰色的毛衣,看起来很帅。
Tā chuān le yí jiàn huīsè de máoyī, kàn qǐlái hěn shuài.
He wore a gray sweater and looked very handsome.
这面墙刷成灰的吧,比较耐脏。
Zhè miàn qiáng shuā chéng huī de ba, bǐjiào nàizāng.
Let's paint this wall gray; it's more dirt-resistant.