Let’s step into the wayback machine and talk about some research that even the psychologists among us might not be aware of (I certainly wasn’t). It seems that at the turn of the 20th century, many psychologists and psychophysicists (including the father of psychophysics, Gustave Fechner) were interested in aesthetics. Out of this interest came the idea, inspired by the work of Helmholtz and others, that geometrical figures had a certain “energy,” which influenced the subjective quality of their combinations. For some reason, this idea reminded one psychologist, E. Bullough1, of what he believed to be a “decorative canon”: “that dark colours should stand before light ones.” Bullough believed that this canon was the result of different colors having different weights (which he saw as analogous to the energies of geometrical figures). Here’s how he describes the weight of colors:

Supposing a wall 10ft. high were to be painted in two different shades of one colour, viz. pink and red, in such a way that both would be in equal proportions, the one occupying the space below the other; should the red be placed below, up to 5 ft. from the floor, and the remaining 5 ft. be painted pink, or should the position of the colours be reversed? It is pretty safe to say that the former course would be adopted. The effect of 5 ft. of red on the top of 5 ft. of pink would give the majority of people an uncomfortable feeling of top-heaviness, instability and lack of balance, which would be absent from the reverse arrangement of the colors. (p. 112)

In order to test whether the “decorative canon,” and its implications for the weight of colors, had any objective basis, Bullough conducted the following experiment. He put together a bunch of figures like these:

He asked participants, among other things, which ones they liked better, and found that people preferred light colors on top and dark colors on the bottom, confirming his “decorative canon,” and his belief that colors have weights, with dark colors weighing more than light ones.

Following up on Bullough’s study, several researchers over the next few decades further explored the weights of colors. Most of these experiments used setups like this one2:

I know that’s kind of small, but the two circles (labled G and H) represent holes behind which colored glass would be placed. The line between the represents a fulcrum, and participants would be asked to move a pointer on the line to the position at which they believe the fulcrum should be balanced. Thus if the color in one circle was perceived as heavier than the one in the other circle, participants would move the pointer closer to the heavier color. Using this method, Marion Monroe3 found:

• Overall, blue is heavier than red, red is heavier than green, and green is heavier than yellow.
• Brighter colors weigh less than darker ones.
• Increasing saturation makes colors appear to weigh less.
• Brighter backgrounds make dark colors look lighter (less heavy) and bright colors look heavier.

Monroe also discovered an illusion. When participants judged the midpoint of the line between the two circles, they tended to perceive it to be closer to the heavier color than to the lighter (less heavy) color.

Pinkerton and Humphrey4, using more sophisticated analyses, got slightly different results. Using the fulcrum method, they found that red was consistently the heaviest color, followed by blue, green, orange, and yellow, again confirming that darker colors are heavier than light ones, but they found no effect of brightness. Here are their average heaviness rankings (1 = heaviest, 4 = least heavy; from their Table 2):

Going with the latest and most sophisticated study, then, we can conclude that red is the heaviest color studied so far, and yellow the least heavy. As far as I can tell, no one has come up with anything resembling a plausible hypothesis for why some colors look heavier than others (unless you want to run with the “energies” thing), much less tested such an hypothesis. We do know that the weights of colors don’t affect the weights of objects (e.g., red objects don’t appear to weigh more than otherwise identical yellow objects)5, so the effect seems to be just about the color. That might provide a clue. Unfortunately, the literature trail seems to have gone cold with Pinker and Humphreys 1974 paper, so it may be a while before we learn anything more about color weights.

1Bullough, E. (1907). On the apparent heaviness of colors British Journal of Psychology, 2, 111-152.
²Monroe, M. (1925). The apparent weight of color and correlated phenomena. The American Journal of Psychology, 36(2), 192-206.
³Ibid.
⁴Pinkerton, E., & Humphrey, N. (1974). The apparent heaviness of colours. Nature, 250(5462), 164-165.
⁵Payne Jr., C. (1958). Apparent weight as a function of color. The American Journal of Psychology, 71(4), 725-730.