First question.. where are the reds in the backglass??? If any are in the illuminated areas then you need to make a translucent paint.
Any silk screen supplier can sell you screening enamels ( this is what the BG would have been screened with originally), you will need your colour and you will need a clear base.
Mix your colour to match and then put both BG and a small piece of glass over a light source.. you can then mix your paint with the clear onto the spare glass and match its translucency also... once done - spray away to the BG.
ALL backglasses are screened with a translucent paint to begin with.. once this is done, the blockout is put on the back to make it a solid colour instead
