Cocks have a slightly broader bill when viewed from the top. Their colour on the head is marginally lighter as well (cock on right)

In side-profile the bill is more thick-set as well. Also the hens face colour is nearer to black the cock nearer to red-brown. Also on the cock there is a much clearer distinction where the colour of the face and the colour of the crown come together, less distinct on the hen.

Cocks also have a much more chestnut ting to the breast, less so in the hens. Belly also slightly brighter. Cock on right.

In good sunlight the cock will have much brighter rump and tail-feathers. Not so obvious on this hen as she is plucked but you get the idea.