Colors are washed out in Unreal, but not in the Rive editor.

[Tod-Rive]

This seems to be a color space issue for some users, but it's not correctable by toggling the sRGB option on the texture. We need to look into this.

[BuhDan]

I'm getting this issue as well.

Colors inside of Rive, in my example here to the left #730000, import as hex linear.
You can see that as the bright red to the right of the image. That is the imported Rive file.

Overlaying a border (highlighted) set to hex linear 2C0000 matches sRGB 730000 and it displays as expected.

This is using a Rive Widget inside Unreal 5.3.2 with Rive version 0.3.7a-gh.
This behavior was not seen in Rive 0.1.17 and Unreal 5.3.2

[Tod-Rive]

This is definitely an issue. We're refactoring the Unreal plugin and rendering right now. I suspect this will be fixed as part of the refactor. If not, then soon after.