Here's the colour-tweak I promised.
Before tweaking the colours, I removed the highlights from the bricks, as they were adding needless, distracting noise and making the foreground harder to discern. I also darkened the background and some of the non-interactive(?) background elements such as the mounted heads to make the foreground elements stand out better.
Your tiles have a very high colour count, which made editing the colours difficult, so I ended up doing what I could with some overlay layers. Since the castle is meant to be "undead" and falling apart, I went for a green cast over most of it, with a bit of blue. I kept the wood reddish in comparison, so that it stands out well, making it easy for the player to know where they can go. I didn't want to add more colours or change your pixel work too much, but here are some ideas for additional changes you could make:
- have the vines on the table also creep along the floor. Those colours would make the floor pop better and give the castle more of an abandoned feel. Even if you just do some colour tweaks along the top few pixels of the floor instead of drawing out the vines in detail, it could look good.
- Make the map(?) at the top contrast less from the wall, unless it's interactive. Even with my colour tweaks, it's still distracting.
- Have some glow on the bricks from the window(?) and around other light sources, like the candles. Not full circles of light, just some highlights.
I mentioned your high colour counts. Is there reason for those? Tiles with so many colours are harder to author, and even harder to edit.
