light-yellow color
緗 centers on a specific light-yellow color, often associated with silk or fabric. The meaning is narrow and concrete, without major abstract extensions.
緗 combines 糸 (silk/thread) with 相, which likely contributes the sound. The character is used for a light-yellow color, possibly originally referring to the color of silk.
The left side 糸 suggests silk or thread, and the right side 相 can remind you of 'mutual' or 'aspect'. Imagine a bolt of silk dyed a mutual shade between white and yellow: a light-yellow color.
For ショウ, picture a light-yellow silk scarf being shown off: show -> ショウ, and the scarf displays the exact light-yellow color of 緗.