Negative FRER pics below

I took a test last night using a blue dye test but didnt see a line... I tested with fmu with the same blue dye and I could see the faintest line. Just a few minutes ago I tested with smu with FRER and i didnt see anything. What's going on??

With fmu

Smu FRER

This pic is only to show that it was actually a line on it