Wow, how cool is that. My mare gave birth to a bay filly last year and I was convinced it would be chestnut, as sire was chestnut and all his offspring have been chestnut no matter what colour the mares have been. According to the calculator my filly was destined to be bay. So it seems to have been correct on this occasion.
Last year we put our Bay Mare to a Bay Stallion and using the calculator it reads
87.89% Bay 6.25% Chestnut 5.86% Black
We've had a chestnut filly, I was suprised we had a chestnut but when I went on Llanarth Stud's website one of Llanarth Alleycat's (the Sire) prolific winners is a chestnut mare.
My grey mare has had three foals to grey stallions nad one is a grey filly and the other two are bay fillies; according to the calculation there shouldn't be a bay!
As far as I can see the bay colour comes from the famous Hanan as I think she is the nearest bay in the pedigree.