The following is a list of CC I use on my horses. If you purchase a horse from me, you will need to have these markings downloaded in order for the horse to show up properly. It's honestly kind of tough to figure out which markings are from which package file in game, but if you horse doesn't look right, let me know and I will scour the files for you. I will try to keep this updated as I add more content to my game.

No-Shine Tails - Equus-Sims
Custom Eyes - Silver Dragon
100 Layers Mod - Spotted Acres

No-Shine Tails - Equus-Sims
Custom Eyes - Silver Dragon

Diamond Shaped Blaze, over the chin - Equus-Sims
Snip - Equus-Sims
Big Blaze - Illusion Equestrian
Clean Broad Blaze - Illusion Equestrian
Stripe - Illusion Equestrian
Star and Snip - Illusion Equestrian
Face Markings - Spotted Acres
Massive Set of Face Markings - Silver Dragon Estates

Large Facial Markings Pack - Christina Lindblad
Disconnected stripe, uncentered stripe, partial coronet - Thunder Ridge 
Dapples (download here) - Malory McLain (the download link on the forum is broken so I uploaded it myself)

Full Body Marking - Silver Dragon Estate
Primitive Markings - PharoahHound
Roan Markings - PharoahHound
HD Splotches-Walden

Appaloosa Mottling - Illusion Equestrian
Regional Tobiano - Illusion Equestrian
9 Splotches - PharoahHound
Spots - PharoahHound

Mix&Match, splash, and regional overo - Thunder Ridge 

SLIDERS (not required) 
Leg size slider - PharoahHound
Tail thickness mod - Pharoahhound
Horse size slider - Paragon Farm
Head size, Belly width and Muzzle size sliders - Pharoahhound

Draft neck, flagged tail, & neck curvature - Eyelet