Considering that most TB's are bays/chetnuts - and this breed is based on
three early Arab bloodlines crossed with local horses - deliberate color
selection is stongly indicated.
I've observed that in excessive heat & humidity conditions most
chestnut/bays seem to suffer more than the greys. Dark colors attract
more bugs! True--those annoying flies that burrow in to the chest,
ticks, gnats--all seem to dive for the darker horses in the field first.
Chestnuts are especially prone to sunburn (they are redheads after all).
I have seen more skin disorders on darker colored horses than greys.
True some greys, but certainly not all, can develop melanomas--but so did
my dark bay Morgan.
I'm not sure we can draw any reasonable conclusions from the observations
so far. One observation--at last year's Old Dominion 100, 41 started and
only 10 finished. Of that 10, 9 were greys, one was chestnut. It was
record heat and humidity--can that tell us something?
Diane @ Safe Haven (with one of each--grey, redhead, bay)