You're right I suspect, the dark lines will be lower levels and...

You're right I suspect, the dark lines will be lower levels and damper (hence the darker colour). The wall next to Pond 3 would be stripping of the base, hence the wide width (the wall narrows towards the top in a trapezoidal shape). I think the wall to the north is narrower as it's an internal wall between Pond 3 and 4, rather than a larger external wall. The southern Pond 3 wall could also be wider as an access road or something similar, so worth keeping an eye on progress there.

I'd really like to see the company providing more regular updates on construction progress so we don't have to go fishing for satellite imagery, but good work everyone on digging it up and providing some analysis.

Side note, contacted the company multiple times seeking construction updates and got no response, very disappointing. Hopefully we get a substantial update on Thursday.