TTF fonts use wrong color for antialiasing
This problem is most noticeable when using a font with a color other than black or white (only applies to TTF fonts with antialiasing enabled).
How it looks in Solarus:
How it looks in GIMP:
It is easier to see when zoomed in (the top one is from Solarus). The pixels around the edges where antialiasing occurs should be shades of red but instead appear to be shades of grey.
The problem may be related to what @stdgregwar mentioned in discord about pre-multiplied alpha vs straight alpha.
Possibly related to issue #1389 (closed) (may explain why TTF fonts are not appearing as bold as they should).
The images from Solarus come from version 1.6.0 running on MacOS, but the problem also exists on Ubuntu with solarus-dev branch.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information