We are a warmblood breeding farm so we plan to train her until she is sold. Most of our horses are bred for dressage, and we have a few with some jumper genes too. We have 5 (possibly 6) foals coming next year but she is the only one due this spring so she will get LOTS of attention!
It all comes down to him being homozygous or heterozygous for agouti. If he has two copies of the agouti gene (homozygous), then you are going to have either a bay or a chestnut (given we don't know if he and your mare are homozygous for black too).
She has only had one filly, who is a very dark brown, so that would mean she will be a bay? I tried to follow all of that genetic stuff in college but could never get a handle on it. That's why I went into the hands on stuff for a career ;)
It's really hard to guess. I am certain the foal will be black, brown or chestnut. None of the foals listed for that stallion are red based, which could indicate that he is homozygous for black, but he hasn't produced enough foals to really be able to make that call. I think it is likely the foal won't be chestnut, but not going to bet my house on it. My guess is for a brown foal. Pretty sure the foal won't be bay - the sire is definitely brown, not bay, and brown is recessive to bay.