noun-modifying (irregular)
Prenominal adjective describing something that has a blackish or dark tinge. Often used for colors, shadows, or objects with a dark cast.
彼女は黒みがかった髪をしている。
She has blackish hair.
空が黒みがかった雲で覆われている。
The sky is covered with darkish clouds.
黒っぽい is a more common i-adjective meaning 'blackish' or 'darkish', while 黒みがかった is a prenominal form that sounds slightly more descriptive or literary.
From 黒み (blackness) + がかった (past form of がかる, 'to be tinged with').