Can I use shampoo for blonds on my dr. brown hair?

You can use shampoo for blondes, but be aware that such shampoos often contain mild bleaching agents like chamomille. While they won't damage your hair, they may subtly lighten the brown color of your hair with repeated use.

As far as dying over the blonde streaks, you can do it. However, since they've already been processed I would use either a pigment-only dye such as Manic Panic, or go and see a stylist to have a toner applied. Using a hair dye that contains processors could cause unpredictable damage to the already-processed hair, and may cause it to break off or fall out.

Call the 1-800# on the box of hair dye, they're the hair color expert they can advice you best.