I own every single one of those halters, LOL!
Baby Pink: Rain
Baby Blue: Dreamer
Pastel Green: Joey
Pastel Purple: Miakoda
The only reason Dreamer looks good with the baby blue is because of his blue eye. If he was brown eyed I would not have put that color on him. Miakoda doesn't look phenominal in the Pastel Purple either. I bought her a regular purple instead =)
And don't feel bad about the sorrel/chestnut thing. Everyone has a different view on it, LOL! I was taught the colors backwards... so I would have called him a Chestnut too. Infact, I still call Skippy! Chestnut, though he is sorrel by definition.
By APHA standards:
Chestnut: body color dark red or brownish red; range from very light to liver chestnut; liver chestnut can be distinguished from black or brown only by the bronze or copper highlights on the legs; mane and tail usually dark red or brownish red, but may be flaxen.
Sorrel: body color reddish or copper-red; mane and tail usually same color as body, but may be flaxen or very dark brown.
Anywhoo... i'll get on point, LOL!
For your horse, I think that Hunter Green would look very sharp. Royal Blue would also be nice. I wouldn't recommend Pastels because it wouldn't compliment his coloring. Bold Colors are my suggestion!
Here is the Weaver Graphite Line:
Its amazing what a small difference in hue can do for a horse's coat!
I'm also big on selecting the right Leadline. Here are the Graphic Leads:
I think the Blue Graphite Halter with the Black/Blue/Green would look really sharp on him =)
So there's my two cents!