Export to PDF from layout changes colors #42935

Describe the bug

How to Reproduce

1. Go to 'Layout'

2. Click on 'export to PDF'

3. Click on the link 'generated in the message bar to open file'

4. See error --> Colors originally used in Map Canvas Legend are different than the exported to PDF, while if exported to image, colors are correctly printed as they are in Map Canvas Legend

5. PDF

6. PNG

7. QGIS 3.16 and OS Windows 10 Enterprise

Additional context