Can you change the extension of all files *. PNG?
This will provide the following benefits:
1. Сompression (reduce size of images)
2. Alpha channel (transparency) - it allows to use the effect of smooth shadows, glow, ...
3. Full-color images (At this moment we can't use black, blue, pink colors)
As an example of a sprite of rocket:
PNG

BMP
*.BMP into *.PNG
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MikuAuahDark
create your skins as PNG files
Oh, and the alpha channel will load correctly provided that BlitzMax's PNG loading code checks it's sig bytes correctly.