I love these color questions,,Keep them coming,,,LOL
Ok you have a 50/50 chance of palomino or chestnut. You can not have a dun or buckskin because neither the mare or the stud have the bay gene which is needed to have a buckskin.
A cremello or perlino (double dilutes) crossed with a chestnut will ALWAYS give you a palomino. Or with a homozygous bay (bay gene not black gene) will always give you a buckskin.
The chestnut has to be homozygous or it wouldnt be chestnut.
Punnet squares are not always square. The chestnut has 2 of the same genes which means it is homozygous, we know this because chestnut are always homozygous. S you can use 1 C to represent the mare. The stud has the chestnut gene and the dilute gene because it is a palomino so you need a C and a D if you put these in the column area of a graph paper and the mare's C in the first rom you can multiply them so you would end up with CC or CD so that is 50/50 for chestnut or palomino