AAHHHHHHHHHHH, soapy water!!!!!!!!!! Please tell me you didn't try bleach like one of my customers did! Best bet is to try to get a dye match from one of the high street shoe repair shops. These have a new type of permanent dye now, which has a preparation treatment with it. It may mean you dying both boots with a very weak mix but it should cover well, If you just want the stained area dyed, then you should do a test patch first if it is a large stain. Ask the shoe repair guy for advice on the types of dye. One or two of my customers in the past have had insurance on their charge cards that covers the items purchased and they have been able to claim on that, if they are an expensive pair, you could claim on your house contents insurance, depends on their value and the policy excess.