Opk experienced users

Ok ladies.. I'm fairly new to the opks.. I started day 16 like the insert said to.. so that day was

Day 16 10/1 wed

Day 17 10/2 thur

Day 18 10/3 fri

Day 19 10/3 sat

I believe day 16 & 17 are neg

Day 18 & 19 are positive

I bd on day 16 wed alsi haf ewcm

Day 17 ewcm

Day 18 ewcm

And tonight will bd again.

***but here is my question, I took two opks on wed thurs and fri one at 4a and 3p so almost 12 hours in between so why does it look like they fade in and out.. darker opks are the 4a and 3 p are lighter

So will I ovulate today or what