Genuinely asking about evaps

I’ve been trying to do research and have not found a straight forward answer. I understand evaps typically have no color and look thinner than the control like. Here is my question:

Can evaps have color? I’m speaking about blue dye at the moment I’ve experienced evap/indent with frer. The particular test I’ve used is rexall. I have been seeing a very very faint line within timeframe and then later on (within the hour) it became more distinct I am well aware of the invalidation based on the time frame. This has happened both today and yesterday. 3 days ago I had stark white rexall tests that did not show any lines during and after the time frame. I am waiting until I am a week late to use frer (currently 2 days late)

Thank you 😊

**pics added for reference

During time frame very faint to where camera hardly pics it up

This is what it turns into after the time frame