Hello!

Here is the information provided in the help files about the wavelength option within the Image Simulation tool: 

This is stating that the displayed image will be in RGB format no matter what wavelengths are defined. So, wavelength 1 will correspond to the blue channel no matter what wavelength is defined in the system explorer. You can also try this by adding two other wavelengths in the system explorer and observing that wavelength 1 still corresponds to blue, wavelength 2 corresponds to green, and wavelength 3 corresponds to red no matter what is defined in the system explorer. 

Hope this helps!