I’m currently working on bringing my mare’s tail back from a year of “well you’re a pasture and pleasure pet so your tail can be whatever color it wants”.
Ketchup worked to brighten it but didn’t really improve the color.
So far daily washing with shampoo and dawn dish soap (blue), followed by a deep conditioner have brought the color back to its normal off white shade. I’ll first wash with the shampoo, rinse, then the dawn to ensure that the dawn is only “focusing” on the stained parts. I make sure the conditioner is 110% rinsed from the tail then spray it heavily with Healthy Haircare Hair Moisturizer. This has helped keep my mares tail from getting too dirty between washes.
I alternate between the purple shampoo and conditioner from Sally’s (whichever one is on sale), VO5 Strawberry, and Mane 'N Tail original. The purple shampoo and dawn both will get left in for around 5 minutes while I either wash her body or start cleaning my tack.
My trainer loves using a bleach and water mixture in the tail right before shows but my girl already has a ratty looking tail so I don’t want to risk drying it out.