I've had these ideas sitting in my head for ages so I thought I'd finally post 'em somewhere!
1. Bloom (Blm/blm) - A gene closely related to Sift and Moss that causes colorful ticking to appear across a trotter's top- and midline. This marking can come in any bright or pastel color. (Though poorly drawn here, the idea is to add 'flowers' to Moss' 'leaves'.)
2 & 3. Prism (Prm/prm) - A gene that lays a rainbow sheen over a trotter's coat. This marking can cover a trotter's entire coat, or any portion thereof. 2 shows Prism over most of the base coat, 3 shows it restricted to white markings.
Lines courtesy of tikki-tak!