Hello. Why am I losing colours in my tilesets running JJ2 in 16 bit mode?

My tilesets look as intended in 8 bit, but when I run the game in 16 bit I lose colour, as you can see here:

EDIT: WILL LINK ON A REPLY TO THIS POST. Apparently JCF is saying: You are only allowed to post URLs to other sites after you have made 2 posts or more

I`ve tried making two variations of the tileset I finished a few days ago. On the first, I`ve followed the default JJ2 palette. The second, I followed the default JJ2 palette as well BUT checked off the option in JCS for remapping.

I have also tried reducing colours on the tileset itself.

Both still result in the image above. 16 bit mode loses colours.

Especially noticeable on close gradients. The colours in question here are a gradual reduction of 1RGB value each palette slot. Example: "255 255 255 to 254 254 254 to 253 253 253 and so on.

I suspect the colour values are too similar and need more of a gap instead of only going down 1 increment, but thought I`d ask here first instead of revamping my project(yet again )

Thoughts? Ideas? Possible to fix from my side?

Thank you for reading.