Chestnut x chestnut always gives you another chestnut. The flaxen is a bit more complicated - it's thought only to express on chestnuts and may be a recessive gene so you'd need two flaxen chestnuts to produce a flaxen chestnut foal. I will have a look and see if there's any more recent info about it though.
The sabino is a bit of a lottery - could be one jagged sock and a little white on the face or it could be four big stockings, big white face, belly splashes, splashes of white up the shoulder and flank, and lots of roaning. Interestingly it seems to express more loudly on chestnut than bay or black a lot of the time.
Every time I learn something new it pushes some old stuff out of my brain!