Discoloring on bike frame after primer

I am in the process of repainting my steel bike frame. I had the frame media-blasted and applied an initial coat of 2k primer. Today, I wet-sanded with 400 grit, cleaned with soap and water, cleaned with rubbing alcohol, and put on a second coat of 2k primer.

I was concerned about the inside of the frame getting wet and rusting, and so I also sprayed PB rust blaster inside the frame prior to wet sanding. However, I now see discoloration of the primer around where I sprayed the rust blaster.

Two question:
1) What, if anything, should I do about this? Is this a problem?
2) What should I have done differently and what should I do moving forward (e.g. prior to paint coats)? Given that I am wet sanding, I need a way to clean the frame after sanding. I did pick up some TSP Substitute; should I use that after wet sanding instead of more soap/water and just avoid using the PB blaster until I have done with the paint and clear coat?

Thanks!