Hi- I have invested in 3 white so called Firestone28x3 non-skid for my 1916 HD outfit only to discover that they have turned brown. Tried to wash with solvent and some detergent but seems to be impossible to restore. Bike has not seen real road usage yet. Any advice?- are they just crap?- the price suggest differently- they were bought from Coker. The most brown tires were put on 1 year ago.