black
黝 centers on a deep, dark black, often with a bluish or greenish undertone. The given meaning 'black' captures its core sense of a very dark color.
黝 combines 黑 (black) with 幼, which likely contributes the sound. The character expresses a deep black color.
The left side 黑 means black, and the right side 幼 suggests something young or immature. Imagine a young, fresh black dye that is especially deep and dark.
For ユウ, picture a deep black you: you -> ユウ, as if the color is so dark it absorbs your reflection.