heads of grain, cleverness
穎 centers on the tip of a grain ear, the pointed end that stands out. The cleverness sense extends this idea to a sharp, outstanding mind.
穎 combines 禾 (grain) with 頃, which likely contributes the sound and the idea of a head or tip, together suggesting the pointed tip of a grain ear.
The left side shows a grain plant 禾 with a 匕 (spoon-like) tip, and the right side 頁 (head) emphasizes the head of the grain. Picture the sharp, clever tip of a grain ear standing out.
For エイ, imagine an 'A' grade grain ear with a cleverly sharp tip: 'A' -> エイ, the outstanding head of the crop.