OK, it seems I can finally put the scattering issue to rest (at least for a while).
The way I see it we have two cases:
- No haze/fog in the air. Rayleigh scattering dominates. This is strongly wavelength dependent; the scattering of violet light is nearly 10 times greater than that of red. The scattering is relatively weak however and will not cause significant extinction unless the distance is large.
- Haze/fog present. Mie scattering dominates. Not strongly wavelength dependent, so all visible light will be scattered fairly equally. Clouds are white after all, right?