Waterproof Membrane

I cannot find any information on this. I have waterproofed my bathroom a few weeks ago and whenever the waterproof membrane gets wet in any area it goes a lighter blue colour. Any ideas why? Thank you in advance. The product I have used is betta. Primed and followed instructions to the ultimate.

May be late for this reply, but waterproof membranes can change colour as they may water stain. It doesn't impact the membrane performance as these types of products are designed to be covered over so colour stability is not the same as outdoor coatings. Unless the membrane is changing nature, e.g. going soft and mushy then you have no issues for tiling over.