Yet a red barn still appears to be red and grass still looks green, as long as there's enough light for you to see, and as long as you know what you're seeing. This is important to realize. Beginners usually paint colors equally bright, no matter how far or how near they may be, and no matter what kind of weather they are painting. They simply go by the name of a hue and not by its actual appearance, its value. They'll paint the red barn, the green grass and foliage, as seen from close-by, in bright sunlight.
Beginners merely paint the sky blue on a sunny day, gray on a rainy day, dark blue towards evening.
The mental approach toward color perspective is identical with the approach to learning linear perspective. A distance of a few feet doesn't change colors in a noticeable manner. You need the outdoors for observing color differences. A view from the top of a hill over a vast panorama is the most striking proof of how hues are affected by distance and by weather. Take photographs of the same view on the two different occasions or, better yet, make color sketches, concentrating on shades of colors, rather than fine details.