Another colour question

[Thistle]

Just working out possible foal colours. Need to work out if mare carries agouti.

Mare is bright bay, 1 parent is chestnut, other is unknown (surprise pregnancy, thought to be sec D as there was a sec D stallion nearby)

Am I right in thinking the mare is heterozygous for agouti as for her to be bay she would have got it from father as her dam is chestnut so not carrying agouti?

Also sire of as yet unborn foal is darkish bay, his sire is black (Fleetwater Opposition) and his dam is dark bay. He must carry a chestnut gene as he has produced chestnut foals, some of his foals also appear to be black so would he also be likely to be heterozygous for agouti?

I have worked out high probability of bay foal with possible black or chestnut, is this correct?

 

[Meowy Catkin]

If the mare is bay, then she does have the agouti gene.

Her chestnut parent would only pass on chestut to her, so the black gene must have come from the unknown parent. Chestnuts can have the agouti gene, but it doesn't change the colour of their coat.