Evap common for FR?

I took this test beginning of the week in the middle of the night and couldn't  see anything.  By day time if I squinted right I could see a barely noticeable line.i know I know shouldn't read it after ten minutes.  Forgot the test in my car for a few days and saw the line got darker.  My question is how common are evaps on First Response? And do they normally get darker?  Also to see the line better you have to zoom in on the pic.