How can depth be created through blending warm and cool colours?

Correct answer: By using warm colours to advance and cool colours to recede

The governing concept is colour temperature and atmospheric depth. Warm hues such as reds and oranges generally appear to advance, while cool hues such as blues and blue-greens often seem to recede. A controlled blend can therefore make the foreground warmer and the background cooler, creating spatial separation. Using one colour, only white, or blackening every colour does not establish this temperature-based depth.