Our brain uses a number of tricks to gauge distance. One is noticing that when we see a range of hills, the further away they are, the lighter they become. Next time you see rolling hills, notice how the one behind always appears slightly lighter than the one in front.
Above are some I prepared earlier in Wales. The foreground is rich in colour and dark, but the exact same habitat appears much lighter on the more distant hills, getting closer to white with increasing distance. This effect occurs even on days with no cloud.