This is what we call marbeling.
It can happen if your mix ratio is slightly different between beads.
You need to be very precise and consistent with your mix ratio when working with an opaque powder in zones 2 & 3.
Also when applying, it is always best to overlap zone 2 slightly with your zone 3 bead, after making sure your zone 2 bead is flush to the natural nail.....(if there is a ridge then this will definitely show through as a shadow line).... then press & guide it down the nail. That can stop this problem. HTH
Have a look at the custom blend tutorials on here, as I find the Flawless Pink just a bit too peachy pink for a lot of clients I prefer the base mix (with a few tweaks)that GMG talks about on there, it gives a more natural look.