Major vs. Minor

Maj7 chords are inherently round, no matter what the color is. By the same token, 7 chords (like A7) are inherently angular. So, A maj7 is like a round nebula (or cloud or bubble) of pale red (A), deep orangish (C#) and pale blue (E). As a chord, sounds red with darker edges, purple perhaps, sometimes dark orange, depending on what comes aftetwards.

Dominique, did you see the thing in Harper's a month or so back where some dude in the 1700s did an analysis exactly like that??

I did not. In fact, I've never actually done this myself until now - I was surprised to see that my conception of the colors of notes from chord to chord doesn't change that much!

I think that's part of it - I think of chords in terms of how they appear on piano. Were I guitar player, I might think of them differently. However, I do suspect that the chords I believe I know the least about tend to be darker. Ab, Bb, Db - for my fingers, it is more difficult to play in these keys on piano, so I have written less in them than others like C, F, D, G - perhaps Bb minor is also kind of impractical on guitar. I have something of a fetish for F#, and perhaps I view E as something of a hybrid of F# and C, which in my mind are somehow like yin and yang. This is getting into stuff that even I don't have the patience to elaborate on, but I guess I'm saying I can see why my descriptions would necessarily not always translate.

One nice thing about the guitar is that if a moveable chord shape is practicable, then pretty much any position for it is practicable. So Bb minor isn't any more or less difficult than B minor, C minor, A minor, etc. (presuming you're using a barre shape and moving it up and down the neck).

A standard-tuned guitar loves the key of E partly because it's the guitar's lowest note (which makes it easy to use as a drone and gives you a convenient starting and ending note) and partly because the open strings suggest E. But in a loose sense, all keys are equally easy (or, if you prefer, equally hard) assuming you ignore open strings and focus on moveable shapes. This is not so on a keyboard.

which, come to think of it, any electronic keyboardist can do, too. and which, come to think of it, irving berlin, who only knew how to play in one key, also did, way back in the day.