Choose only ONE .pak among all the folders.

01 Replace the default dark black coat for a black bay one
02 Replace the default light black coat for a black bay one
03 Replace the default grey coat for a black bay one. Tulpar and Sleipnir will become grey instead (all "light black" horses will turn grey) for keep coats diversity.
04 Replace the default white coat for a black bay one. Change the default light black coats (buyable ones Tulpar and Sleipnir) for default white coats.

Simply Extract files and put the .pak you want into the following folders:
KingdomComeDeliverance\Data\_fastload
KingdomComeDeliverance\Data
(If you're under steam you'll find this in C:\Program Files (x86)\Steam\steamapps\common\)
Don't forget to put the .pak in BOTH path