Np at all! If level design is new to you you did a knockout job of it, as it's quite involving. I'm impressed.
Regarding the dithering, if you're taking suggestions I'd personally do away with it in favour of a palette order inversion when above ground vs when underground so that every sprite looks like it's being strongly shaded by the sun. It's an old trick that still looks quite clean, though I don't know how it'd work with 3 + 1 highlight colour vs 4 shades of the same colour.