from my experience with neon inks, you want a stong white underneath the ink for maximum vibrancy. The neon inks don't seem to be very opaque, so the strength of the white underbase will determine how intense the neon ink prints. the under base doesn't need to be super bright white as that often means you have a thick print. We do one stroke for the white underbase on an auto and get great vibrancy with the neon top colours.
if you are printing manually and find one pass of the underbase is not giving a strong enough white and you want to do a print/flash/print, i suggest trying to minimize ink deposit as to not get a thick print.
if you are printing manually and find one pass of the underbase is not giving a strong enough white and you want to do a print/flash/print, i suggest trying to minimize ink deposit as to not get a thick print.