Breeding two sheep in one color resulted in offspring in another color.
Happens probably only when breeding multiple colors simultanously.

I have built several pens using fences. Put a pair of sheep in each, one color in each pen.
Then gave them all wheat.
Result is that sometimes offspring got different color than their parents.
Screenshots after breeding attached.

Last screenshot is an overview of all pens. One can see that red sheep pen is not adjacent to cyan pen, so it was not possible that cyan sheep bred near the fence and offspring got created on the other side of the pen. Glitching through two fences at once is rather improbable too.