Light levels on other celestial bodies
You don't need to do it that complicated. The sunlight's spectrum is the same everywhere in the solar system. And in order to get the light intensity, you can simply apply the inverse square law that intensity drops to 1/4 if you double the distance to the sun - like you did for getting the irradiance. The spectral sensitivity of the human eye is also the same everywhere in the solar system.

What is different, is the local conditions: On the surface of bodies it is, of course, influenced by the atmosphere - and that is likely the most important aspect when you want to model different colour; this does include possible aerosol content (like you see for instance on Mars during dust storms). The 2nd most important impact probably is the colour of the light reflected from the body you are "standing" on, thus a feature of the surface material.

So in order to get the colour impression you have to account for these two spectral filters, applied to the (nearly) black-body distribution of the sunlight. Thus in your equation you need to insert these factors as well - or just look at these separately as your equation states the default. Unfortunately this opens a VERY wide field as you can have a variety of atmospheric compositions - just think of the different light conditions you can have here on Earth - and now add the factor of completely different chemestry in the atmosphere. Modelling that is definitely an ongoing scientific endeavour.

If your quest is "just" to get some artists impression, play around with different materials and adjust the spectral transmission and scatter properties of the atmospheres (especially that) - and the ground material.