Never had tint spray go brown ever.

You are sposed to be able to use a cellulose based paint as it can still let light through. TBH though I'd just pop your Lexus jobs on E-bay and put it down to being a bad idea and then tint some standard lenses yourself. It isn't hard and the spray is less than £20. Preperation and taking your time to do the job right will ensure a good finish