Originally Posted by BlackHand
everything in your question can be mastered by mastering two skills:
1. color matching (look at the photo or scene)
2. color mixing, paint mixing (make the paint to match the color you see in the photo)
but that does nothing to explain why an artist might select something other than the color observed in the photo. that can be a much more in depth topic. it is also worth noting that staring into the sun is not something that can be reproduced with selecting a hue and value from a tube of paint. fluorescent colors convert ultra-violet light energy into visible light energy thus increasing brightness beyond the limits of the daylight being observed. an artist with mastery and understanding of many things is not limited to painting only what is actually observed. they can do anything they desire for any reason. colored light and the illusion of darkness can drastically change the actual colors of paint used to imply the perception of natural spaces, lights, scenes, objects etc..don't worry about this at first. it is right there in the books you will read when you become an advanced student of oil colors.
That is the reason a real artist needs to familiarize him/herself with the limitations of photographs, in order to be able to correct those typical photographic aberrations during the painting process.
Such items as the correct color of a cast shadow in a sunset-type of scene, comes to mind.
Such a color won't show in a photograph, but it should be included in the painting.