User blog comment:GodzillaFan1/Artwork Review: Classic Gooebumps/@comment-28171460-20170717094639/@comment-4207976-20170717193927

>Cool/cold shading

Oh, that's what it's called.

>The blue suggests that the ares is partially in the shadows, but the area should still be reasonably well lit because of the overhead light and the luminous hand.

Well, there's limited amount of room on the cover, and he (Brandon Dorman) probably wanted it to have more color, so he added the cool shading at the bottom.