Is there a difference between brands of antibiotics? ive taken keflex before but its always been the red teva capsules i was prescribed it and got some solid green ones. im worried about an allergic reaction? is it possible?

In the US, generic manufacturers must follow strict Food and Drug Administration rules to assure their drugs are identical chemically and in potency and safety to the same drugs as brand names. You never need insist on the original trade name. Most pharmacies automatically substitute the generic versions unless the doctor's prescription states "no substitution" or similar wording.