It has been getting progressively worse
If you compare ch40 with ch23 or so, the line art is much more polished and a lot cleaner in the latest chapters, but the way the artist colors has changed a lot. The colors seem less saturated and don't have as much highlights/sheen which is probably why it feels like it's gotten flatter over time. The artist probably has found a method for them that's easier to keep consistent and faster to do as they've gone along.
Yes it's just you. You just don't like the new coloring.
Maybe it's just me