I didn't take the second screenshot, I took it from google images.
Some progress: actually it seems that the issue comes with only one LXF file.
When I'm in extended mode, I can see the secondary toolbar for colors, as expected.
Then I open the file (the LXF for modular 10224) and LDD reverts automatically to the regular mode, don't know why. Maybe the file has been created in regular mode and I need to convert it ?