HDMV PGS subtitles' shadow is grey instead of black

Hi, when I play a video with PGS subtitles on Infuse (not just 7.4 but also previous releases) on macOS, the color shadow of the font seems to be grey instead of black, I’ve noticed that it occurs with every PGS subtitles, and doesn’t occur with VobSub subtitles.
This is a comparison of what it looks like vs what it should be like.