Do blue dye tests always give out false positives?

Took a blue dye test yesterday saw a very faint faint line I took a picture of it today and edited the pic a little cause the line wouldn't really show I mean I'm not trying to get to excited or get my hopes up cause I didn't know and I've read that these tests suck I'm going to retest with a different one what do you guys think? I just think it's an evap line.