dr.zeissler, IIRC the Schneider Euro PC uses a Paradise PVC4 for its CGA output and should therefore have the Plantronics ColorPlus compatible 320x200 16 color mode, as well.

It should be possible to get more colors out of pure CGA games by patching int 10h to set Plantronics mode and to initialize the blue/intensity page with a static pattern or picture.
The game itself would draw to the red/green page, as usual.

Alternatively, you can swap the memory mapping of the red/green and blue/intensity pages and initialize the red/green page with a static pattern or picture.
The game would then draw to the blue/intensity page.

This will obviously only yield good results with games that only display a single mostly static scene.