The rule of three is not about juxtaposing any three random elements, it's about taking three things which are related to each other. It's not any three things

The rule of three is not about juxtaposing any three random elements, it's about taking three things which are related to each other. It's not any three things producing harmony, it's a human selecting three things which produce some effect. This is true for rhetoric because the rhetorician has a purpose he wants to achieve. And another nitpick: It seems perfectly possible to pick three colors which don't work well together. If two of the colors clash with each other, it won't matter what the third one is. With a chord, I suppose (without confidence) that it works because you're hearing all three notes together, but that's not how colors work: if you see the two clashing colors side by side, it's not visually pleasing, even if the third color works with each of those clashing colors individually.