Jamieson, Fausset and Brown on Ezekiel 1:7

7. straight feet--that is, straight legs. Not protruding in any part as the legs of an ox, but straight like a man's [Grotius]. Or, like solid pillars; not bending, as man's, at the knee. They glided along, rather than walked. Their movements were all sure, right, and without effort [Kitto, Cyclopedia].

sole ... calf's foot--Henderson hence supposes that "straight feet" implies that they did not project horizontally like men's feet, but vertically as calves' feet. The solid firmness of the round foot of a calf seems to be the point of comparison.

colour--the glittering appearance, indicating God's purity.