I don't know of anyone at any of my (3) barns that use a specific color supplement. For coat condition and shine my barn members often use fish oil, omega threes, flax seed, and maybe a weight supplement if their horse is skinny. Weight supplements usually contain fatty acids which help the coat shine.
Well I want something that boosts palomino color to that pretty gold. She is fading so fast that it's like oh my she looks completely different! And we are supposed to take a photo shoot soon and I want her to look like a princess horse :)
One that I have found that works for my light sorrel and white(she looks like a palomino but is technically speaking not) is paprika. However I started it before she lost her winter coat and have heard it won't work if they are already faded. And she lives on full pasture with only a run in and is NOT blanketed. The only other thing I do to help keep her from fading is use sunscreen on her coat.
Last Year in July(when I wasn't using paprika):
This year pic taken today(Using sun screen and paprika):