Hi Cyrille
Just an idea… Maybe you could use the RGB coloring keeping one channel fixed and mapping the scalars to the two remaining channels? E.g. map scalar 1 to red, scalar 2 to green and keep blue at zero? (For RGB coloring, this might help: https://discourse.paraview.org/t/coloring-surface-by-predefined-rgb-values/6011)
Cheers,
Venke