Question about the control strip

Hi everyone,
I have a quick question. I took two pregnancy tests and unfortunately, both were negative. We've only been trying for a few months, so we know it might take some time. I tested quite early, though, because Tuesday is when my period is due. I'm aware that testing this early isn't always ideal, but the desire to know sometimes overpowers the logic.

The tests were from Sensitest, and one had a very clear red control line, while the other had a clear purple control line. I was wondering if this has any meaning or if it's just coincidence and that there's always a 'dark' control line regardless of the color.
Hopefully, you can answer my question.