What the message means
Snapmaker Orca (like OrcaSlicer and Bambu Studio) only fully imports a .3mf as a project — colors, painted segmentation, plate and object data — when the file's producer tag is on its whitelist (BambuStudio- or OrcaSlicer-). A file made by PrusaSlicer or Creality Print isn't recognized, so Orca falls back to importing bare geometry and discards the color data.
Why repainting by hand isn't the answer
You could re-paint the model triangle by triangle in Orca, but you'll never match the original exactly and it takes ages — every time, for every file.
The fix
Run the file through bedready.io/convert. It re-tags the file as a native Orca project so Snapmaker Orca loads the full color data, translates PrusaSlicer/Creality paint data into Orca's format, and adds the U1 profile. The colors come back, and the file opens as a proper multicolor project.