With a little bit of greenstuff and some bright paints I was able to solve that problem.
It is barely visible in the first picture...
... but when off their bases, the color coding is quite distinct.
And of course I had to designate their spots on the Land Speeder Storm for hassle free loading.
Have you ever done a removable set of miniature and had trouble getting them back in place? I know that this is sometimes a problem in Warhammer Fantasy with regiments and weapons and cloaks pointing every which way. Do you have any tips or tricks to remembering who goes where?