I created my project under jagstudio.

Hello world on Virtual Jaguar OK!

Time to draw an object :
- edit assets.txt
- edit rapinit.s

build and run -> First image on Virtual Jaguar OK!

I even make it scrolls using xadd_ 

hm....wait, it took all the 256 colors, since image is 8bits
On jaguar, you have 256 colors on 16 CLUTS, each 16 colors.
You can load each CLUT one by one or load the 256 colors at once.
For example, your 256 colors background could a part of its pal to a 16 color object.

Let's go for using a 4bpp version of the image and load the CLUT using  jsfLoadClut and /2 on rapinit.s

====

4 hours later, it still doesn't work : screen is pure garbage and I don't know why.

I used several tools to convert my image on 4bpp (because I knew from my Genny experience it could be tricky) but nothing!

Time to ask to the experts => https://forums.atariage.com/topic/372996-how-do-you-handle-4-bits-bitmap/