I will address the colours rather than the to breed or not to breed.
She is black under the grey so you need to know if she carries a red gene. If she does then a pali stud would not be a good choice to avoid getting a chestnut. Pali is chestnut with a cream gene and therefore can only give the foal a copy of the red gene. If your mare carries red then it's 50% that the foal will pop out red based. The stallion has a 50% chance of passing on cream so half the red based foals resulting from this cross will be pali and that leaves you with a one in four chance of chestnut.
If, however, you breed her to a stud that is genetically tested to be homozygous for black, you will never get a chestnut foal.
Then depending on how many copies of the grey gene your mare has, the foal has either 50% or 100% chance of greying out.
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Last edited by blue eyed pony; 01-11-2012 at 10:05 AM.