Your guide looks great, Mini! ^^ I'll go through and see which ones I can help with - some of them I've got little clue on either. XD
May/June: the first group of ponies are usually called the Natural ponies, and the first three of that group are the Chestnut Pony (currently is Brown), Flaxen Chestnut Pony (currently Light Tailed) and Dark Bay Pony (currently Black Tailed).
July: the Paint/Cow horses are the Bay Paint/Cow (currently Brown) and the the Chestnut Paint/Cow (currently Light Brown).
August: no idea what the ponies are called as a group, but I think the unnamed one on top is the Dun Pony and the two on the bottom are the Growing Buckskin and the Buckskin PPS. Rainbow Drafts... *dies* They were mostly called by their face colours, as I recall. In order of appearance, I think they were the Purple-faced, Pink-faced; Hot Pink-faced, Red-faced; Orange-faced, Swirled; Yellow-faced, Green-faced; Teal-faced, Streaked; Light Blue-faced and Dark Blue-faced Rainbow Drafts.
October: for the Roan ponies, the one next to the Blue Roan is the Red Roan, but the other three I'm not sure on. I would guess (from left to right on the top) Bay Roan, Dun Roan and Flaxen Red Roan. No clue on the Splatter horses, but I'm pretty sure the Zombie and Undead ponies are the right way around, with the grey being the Zombie and green being Undead.
January/February: with the Appaloosas, the first two are the Bay Appaloosa (currently Brown) and Chestnut Appaloosa (currently Light Brown). I think the February horses were called Ghost horses, so maybe Purple, Blue, Red, Orange and Orange PPS Ghosts?
March: the horses are called the Natural Horses, and they are (in order of appearance): Bay, Light Bay, Black, Dark Bay, Dark Brown, Liver Chestnut (I think), Chestnut and Palomino.
April: for the Native ponies, I think they're the Bay Native Paint, Chestnut Native Paint, Chestnut Native PPS, White Native Paint and Palomino Native Paint, but that's mostly guessing based on the various things I've seen people call them. XD