red
絳 centers on a deep, rich red color, often associated with silk or fabric. The meaning is straightforward: a specific shade of red.
絳 combines 糸 (silk/thread) with 夅, which likely contributes the sound. The character originally referred to a deep red silk or dye.
The left side is 糸 (thread), and the right side 夅 looks like a person descending. Imagine a bolt of deep red silk being lowered down: 絳 is that rich red color.
For コウ, picture a bolt of red silk being carried by a courier: courier -> コウ, and the silk is a deep crimson red.