Somebody probably said this already, but just to make sure.
Q: How do I change the background, tileset and map name?
A: Open the map you want to edit and select Mapdata(the option is in the top left, next to the list of maps and right beneath Script). However, do NOT edit the Filename yet...
Wait, that's all? Are there no other prerequisites?
I know I haven't shown any of my work so far, but I can work on theoretically simple C++ projects and I can make very atmospheric maps with pretty much any tileset.
Also, my co-worker @haydn_fangirl is a talented musician and artist.
Um, does it also happen when you simply import the sprites to "MyChar"?
If so, it probably happens because "MyChar" uses an indexed 'color mode'. You need to change that to RGB if you want to import all the colors.