Just curious, was the original game also limited to 16 bit color depth, or is this a limitation of the used wrapper (or in fact actually happening)? Looks fine, no problems, was just wondering.

it was 16bpp limited remember we hardly had tnt, gt256, and voodoo 3 graphics card when it was realeased

I've been researching the games texture loader recently. While the textures in the game files are up-to 32bpp, the game only supports loading to 16bpp surfaces. Patching this is complicated.

Patching the game to use a 32bpp Framebuffer is easy (and should be supported already anyway?), but not worth the effort if the textures remain at 16bpp (although it still improves the quality as the color modulation and blending will look a lot better).

The game is also limited to a 16bpp Z-Buffer, but this is easier to patch (and does not have much of an impact on the visual quality).

So with a bit of work, all of these issues could be addressed though.
Not sure if the GOG.com team is willing to invest so much time (= money) for little benefit though.