I was playing around with the "Atari Graphics Studio v2.53" and managed to create some 160x192x4 ".pic" images for the Atarimax Ultimate Multicart for the Atari 5200.
Extract the "Images" folder and place it under the "5200" folder on the SD card.
Also, be sure that your ROM names match the Image names (excluding the .suffix).

Due to the nature of this format, all images are limited to 4 colors.
But see what you think.

https://www.4shared.com/s/fjsHuynbMgm

link is dead.