There are three colors that harmony cannot create; They are red, yellow and blue, the so-called three primary colors. When two original tones are mixed, the number is equal or unequal, and they can produce almost all colors. Any two primary colors are mixed to produce a secondary color (also called composite color): orange comes from red and yellow; Green comes from yellow and blue.

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Google uses one of the three primary colors of red, yellow and blue, and one of the two composite colors: green. But there is no other one: orange.

I think it may have something to do with cold and warm colors. Generally speaking, red and yellow are called warm colors. Blue and green are called cool colors. Then orange is also a warm color. But there are already two warm colors and two cool colors, and one more warm color will upset the balance. So there are no oranges.

You can have a look. There are 4 colors, including 2 blue 1 green and 2 red 1 yellow. In short, it is cold and warm.

Therefore, the color matching of trademarks should be balanced and eye-catching.

All the above are my guesses, which may not be correct. Google's trademark design doesn't necessarily think so much. But as far as human feelings are concerned, it is not unreasonable. Maybe a color expert was consulted when designing.