Will an evap be thin or thick?

I took at test with fmu and at first I got a very faint line,then it very slowly got darker and it was as thick as the control line and it also was the same color as the control line. I had taken test days before and they were negative,even after sitting all day they never got a line on them.

The lighter one showed at around 10minutes then the second pic is when it got darker.