I thought Evap lines were colourless!

I had one without an obvious line at the 7 mins mark. An hour later I saw it with the line. I know I shouldn’t count it as not within the timeframe but I thought evaps were colourless?!

I’m due on today but I’ve average 22-28 day cycles over the last six months. It usually alternates between a high and low number I.e 22 days then 27 days then 24 days then 28 days etc. Last month was 28 days so I expected it a bit earlier this month but instead today is day 28.

Any help appreciated! Has anyone had late positives??