Themis doesn't have a colour wheel...
...It also has multiple simultaneous sensors.
Still has calibration problems because each sensor diode is in a different location wrt the ideal focus and all have different individual responses.
You can't make something that takes instantaneous photos in infinite bandwidth at perfect focus. Something has to be compromised.
In LEO, we can orbit a bus. Round Mars, it costs the same to get a box brownie there.