I've been messing about manually processing images and converting them down to 8 and 16 colours with the STE palette, more out of curiosity than anything else.
I'm beginning to see why I think they didn't bother releasing an ST version, other than the platform slowly dying off.
The big difference between MI1 and MI2 is, MI2 uses scanned hand drawn artwork that requires a fairly good range of colours to reproduce on a computer.
You essentially have to build the backgrounds with consideration for which sprites may be in that scene. And either limit your colour use to allow room for palette entries for the sprites, or hope that some of the sprite colours can be used in your background to help. So my initial thinking was you'd have to use on most scenes just 8 colours for the backgrounds and you'd be left with 8 colours for Guybrush and which ever other character was in the scene also, so maybe 4 colours each (Guybrush would be fixed colours that can't change and will be in every scene).
There are some exceptions:-
Some backgrounds only ever have Guybrush in them, so you could improve these to maybe 12 colours.
Title, intermission and map screens can use the full 16 colours.
You'd need a tool that would take your fixed Guybrush and NPC palette entries, then with those 8 colours and the 8 remaining free colours, analyse, reduce and dither the background so you are making the most of all 16 colours the ST can display. Even then you'd need to think about the player inventory! Ideally you'd probably do a palette split after the play area so you could have a separate selection of colours just for that...phew
Looks to me like the Amiga backgrounds are reduced to 16 colours, no dithering just a simple colour reduction. Leaving 16 colours for everything else, it's a big help.
Anyway, few examples of backgrounds converted to 8 colours:-

- woodstick_result_result.png (85.57 KiB) Viewed 1107 times

- voodoo_result_result.png (43.98 KiB) Viewed 1107 times

- throne_result_result.png (40.95 KiB) Viewed 1107 times

- stans_result_result.png (57.73 KiB) Viewed 1107 times

- spit2_result_result.png (58.54 KiB) Viewed 1107 times

- parents_result_result.png (29.01 KiB) Viewed 1107 times

- marleybed_result_result.png (35.74 KiB) Viewed 1107 times

- mansion_result_result.png (53.19 KiB) Viewed 1107 times

- hotel_result_result.png (28.83 KiB) Viewed 1107 times

- costume_result_result.png (52.11 KiB) Viewed 1107 times

- cemetery_result_result.png (43.78 KiB) Viewed 1107 times

- campfire_result_result.png (58.28 KiB) Viewed 1107 times

- boat_result_result.png (30.47 KiB) Viewed 1107 times

- bedroom_result_result.png (41.01 KiB) Viewed 1107 times

- bar_result_result.png (24.68 KiB) Viewed 1107 times

- phatt_result.png (76.65 KiB) Viewed 1107 times
Couple of 16 colour screens:-

- map_result_result.png (81.84 KiB) Viewed 1107 times

- title_result.png (50.86 KiB) Viewed 1107 times

- scabb_result.png (61.7 KiB) Viewed 1107 times

- Room#0_result.png (75.39 KiB) Viewed 1107 times