While you can adjust the color of the halo at noon, the sun is being affected by the sunset and sunrise automatically. I should also note that the blending is still additive, just in a modified way - so a sun that's darker than the sky will not work for the time being. It wouldn't make a lot of sense anyhow though. The color is the emission from the star as seen from space, but this light has to pass through the atmosphere before it hits the ground. On this way its color changes a little further, so there will never arrive pure white light on the ground, even if the star emits it. The color of the light that arrives on the ground is being calculated using a rather accurate approximation formula. However, if you set the sun to emit orange light you should be able to get orange light on the ground, after all the atmosphere just adjusts the intensities of some wavelengths. The issue that sun and moon pop out will be fixed with the next update, so the first way should work a lot better then. For the viewer height to be really physically correct I'd have to implement some changes as real-life scattering varies with height. This is only really important for planes or mountains though, smaller height differences don't really influence it all that much.