When you turn a photo negative, it just flips all the colors. It doesn't make anything "glow", it's just showing you what's already there in a different color scale, if that make sense. Sometimes it makes it easier to see.
Yes, an evap and an indent can look the same. The question is, did it show up in the time limit? Also, since you're still getting faint positives and are this late in your cycle, it might be time to see a doctor to take bloods.