opks?

Lindsay • married to a wonderful man, have 2 angel babies, and pregnant with our rainbow baby boy

Ok so this is my first month using opks, I started using them the day after I got off my period because I just want to be sure I don't miss it. anyway my question is do they keep getting darker up till the day you ovulate? if anything mine seem to be lighter by the day. top is two days ago, middle is yesterday and bottom is just now. I know these are not positive but do they get darker each day until u get a positive?