As you can see from the chart, my synesthesia is relatively logical. High instruments are lighter-colored than low instruments. Strings are grayish, woodwinds are cool-ish, and brass are warm-ish. I did not include percussive instruments because they are most always bright and abrasive and it’s too late at night to hurt my eyes with those.
Another cool thing about this chart is that you can tell which instruments match well together. For example, if any members of a single instrument class were to create an ensemble (besides woodwinds) they would sound good together. However, if a trumpet player and an oboe player were to play a duet, the sound would be confusing and the warm yellow of the trumpet would clash with the cool yellow of the oboe.
This chart also covers the fact that all woodwinds have very different tones and are only connected by the cool, woody sound. It also proves that a bassoon is a completely different instrument than an oboe and not just a larger version of it. If I were to take the clarinet and put it next to a bass clarinet, they would go well because a bass clarinet is just a darker green than a soprano clarinet. They are members of the same family. However, if the cool yellow oboe mixed with the cool purple bassoon, it might sound awkward and indistinct due to the brown hue created by the match.