Right, I just did a little experiment to solve this purple conundrum once and for all.
It seems that tap water actually makes the reaction go fastest. This is not entirely surprising as imine formation is normally fastest at pH 8. Saturated sodium bicarbonate solution made it go a little pink, though much less than expected. The vinegar, and surprisingly also the vodka appear to show no colour change. Below are some photos, one raw and one to accentuate the colour difference. Apologies for the poor photos, the whole setup is just as amateur as I just wanted to a do a really quick test.