When a JPEG XL image embeds an ICC profile that the decoder can't convert
to sRGB without a color management system, its colors come back as
stored. The PNG the image was stored as left the profile out, so a saved
document or an SVG export held those colors without their color space.
That PNG now carries the profile when it is an RGB one. Colors converted
to sRGB are stored without a profile, as before, and so are a gray
image's colors, which come back as RGB.