Keeping flaxen manes flaxen?

What shampoo do you recommend for keeping flaxen manes flaxen? Both my geldings have beautiful flaxen manes and tails and I would like to keep them that way. My nine year old gelding's amazing white-blonde hair is right now more of a a yellowish color, as it has been nearly all summer (oi x-x) I forget which shampoo I have, but I don't think it ever REALLY worked for getting his long locks clean. There won't be any more baths until the warmth of spring, but I figured I'd ask before I forget. Any suggestions?

Also, whats your favorite detangler? I use Cowboy Magic %100 of the time ^^

When I had a horse, Mane N Tail conditioner. Leave it in and let it absorb. I used Showsheen detangler.

WD-40 also works well as a detangler and really poofs out their manes and tails. Neat effect.

White-n-brite or Orvus works great too!