I was referring to the tile colours, sorry for not being clearer. The shading contrast is fine, the specific colours are just boring because you don't seem to be hue-shifting the shadows. That said, tiles are flat, they probably shouldn't have shading on the edge of each tile.
I meant hue-shift everything towards a certain hue, to various degrees. It's common in pixel art to shift all the shadows and highlights more than the midtones, so that things can retain their colour identity, but the image feels more unified overall. This is part of why you often see palettes that have many different midtones but only a few bright and dark colours.
I think those saturated colours look nicer, but they're too contrasty. This isn't something you can fix with automated adjustments, you'll need to go in and tweak colours separately.
Even "B&W" tiles can work if you're careful with your colour choices. It's common for such tiles to be depicted so that the black is actually a light blue or grey. A good example of this is the opening scene of Who Framed Roger Rabbit, where the B&W kitchen tiles go from
being B&W to being
two very similar colours depending on the need of each particular shot. Of course, to make that work, other very dark colours in the background have to be light. Fortunately, this is actually beneficial since it makes the entire background low-contrast.