I have a flaxen chestnut mare, who after her 1st foal, had her coat change. As she started to shed out, her coat was more liver chestnut than red. Before she always shed out a bright red chestnut, now she's a very dark chestnut.
We have an 11 year old mare that is much darker chestnut this year after she foaled. Of course, her foaling coincided with loosing her winter coat, so who knows if the color change is related to foaling at all.
I have a five year old chestnut mare who changed colors after being bodyclipped this winter. She was a lovely, but regular colored chestnut until she was bodyclipped. Now she has come back as a liver chestnut. It's a definate change in color........I have no idea why!
Many women will tell you that their hair gets darker with each pregnancy as well.....not noticable for those that use a bit of chemical enhancement to their color. My grandmother never cut her hair from the time she was 11 or 12 until just a few months before she died at 88...she had 9 pregnancies with 8 live births and when she took her hair down at night to brush it and then braid it up for the night you could see distinct changes in color for each of those pregnancies and then a steady color until she began getting gray in her late 60's...and finally the almost pure silver she reached at about 75 or so.
This is interesting; my plain chestnut mare who had been the exact same shade of chestnut her entire life, turned a very dark liver chestnut after foaling her first foal at 17 years old.
This winter, her winter coat is a darker shade of red-chestnut than it ever was before having a foal.
We'll see what this summer brings after her second foal is born!