Hey,
This OPK isn't positive yet, so nothing out of thw ordinary yet. You always have low levels of LH in your body and this can show differently on OPKs depending on when you take it, how long since your last wee and how much fluid you have taken in!
Your LH can also fluctuate at various points thoughout your cycle. If it gets darker over the next few days (same as or darker than control line) it could mean a number of things...
It could mean that you may not have ovulated when you thought (some people have surges a few days before their actual LH ovulation surge). Did you ovulate when you normally expect to or earlier?
I've also heard that LH can surge a few days before your period, so it could be that.
Finally, some people find that OPKs can detect HCG (due to its similar makeup to LH) so it could be an early detector of pregnancy. This, however, is not the same for everybody and it goes without saying that OPKs are not relible as HPTs!
From what you have said it is unlikely that the OPK is detecting pregnancy, as you are only 6dpo and have most likely not implanted yet and so you will not have enough hCG to fool an OPK.
I hope this helps!