Unnecessary, redundant colours are discouraged in pixel art. Well-used colours are not. Every colour should serve a purpose and benefit the artwork, and colours which are not well-distinguished from other colours often serve to just make things look blurry or muddy and make it more difficult for the artist to control their work, which is why they're discouraged.
The main changes between the two environments are:
- reduction of reliance on outlines. The new bricks and cobbles rely much more on shadows and highlights to define their forms, whereas the original had a poorer sense of form and everything was defined as shapes with very little sense of form. This change also has the benefit of making the rocks read well without overwhelming the sprites.
- better hue-shifting. The original rocks are all one hue, the original door is just about one hue. The remade rocks have hues ranging from yellow to red (and some pure grey), the remade door also has a broader range of hues, plus the added grey details.
In addition, the remake avoids banding and adds more subtle details with the new colours the GBA allows that the SNES didn't.