white, bright, clear, clean
皭 centers on pure, radiant whiteness: something brilliantly white, bright, clear, and clean. The meanings all extend from this idea of luminous, unblemished white.
皭 combines 白 (white) with 爵, which likely contributes the sound. The character expresses brilliant whiteness or clarity.
The left side 白 means white, and the right side 爵 looks like an ornate vessel. Imagine a pure white ceremonial vessel shining so brightly that it makes everything around it clear and clean.
For シャク, picture a shack in the snow, its white walls gleaming so brightly they look clean and clear: shack -> シャク.