After a bit of digging (forum search led to a thread which mentioned this thread's author) I think I found what you were talking about...
http://www.bay12forums.com/smf/index.php?topic=53429.0So it seems size etc are inherited, size and musculature increase meat gains. His results also indicate colors were inherited.
I downloaded Runesmith to see if it could give me a bit more information about animals - I noticed a correlation between an animal's strength attribute and muscle description but couldn't find any attributes that seemed to correspond to fatness or size. I'm fairly certain these values exist, just that runesmith isn't configured to show them.
That still doesn't completely explain my white cub.
This is the hair color section in the raws for giant leopards: [TL_COLOR_MODIFIER:SPOTS_ORANGE_BLACK:990:BLACK:10:WHITE:1]
Here's the one for cows: [TL_COLOR_MODIFIER:BLACK:1:BROWN:1:WHITE:1:GRAY:1:LIGHT_BROWN:1 (etc, many more colors listed with a weight of 1)
I am 99% certain that the father was my other tame giant leopard. I can think of a few possibilities.
1) The father was actually another giant leopard who was white and wandered onto the map at the right time to impregnate my female
2) There's some recessive trait-like behavior going on
3) There's a chance for colors to be chosen randomly as well as inherited
At this point, without access to that old fort, there's not much more I can do to test that unless I get extremely lucky and end up with a rare color animal again.