To Dye
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means dye so the verb vocab version is to dye.
そめる
You need to dye something that you just sewed (そ) together. It's all sewed and looks like a shirt, but it's colorless. That's where the dying comes in.
髪を何色に染めるか迷っています。
I’m wondering what color to dye my hair.