Another piece of evidence.
I have been using the Marvel Power Grid / Ratings to map out the characters.
Out of the current single characters (each character getting a ranking out of 7), this is the number of occurences of each ranking.
Intelligence - 0 / 13 / 12 / 2 / 3 / 2 / 0. 13 characters have normal intelligence, 23 are learned.
Strength - 0 / 10 / 7 / 7 / 1 / 2 / 5. 10 characters have normal strength, 7 peak human, 7 superhuman.
Speed - 0 / 17 / 9 / 0 / 5 / 0 / 2. 17 have normal speed, 9 superhuman.
Durability - 0 / 10 / 7 / 3 / 0 / 10 / 2. 10 have normal durability, 7 enhanced, 10 superhuman.
Energy Projection - 16 / 0 / 3 / 3 / 7 / 4 / 0. 16 have no energy projection, 7 long range, long duration, single energy type.
Flighting Ability - 0 / 1 / 5 / 13 / 3 / 6 / 2. 13 are experienced fighters, 6 masters of several forms of combat.
Based upon how they are officially described and if we are talking about in game damage, the main ones of interest are fighting ability and maybe energy projection (but even half the characters there have nothing). Intelligence, strength and speed all have the bulk of their characters near the bottom and durability (which True Healing TM) is trying to resolve have a third near the bottom, a third near the top and the rest scattered. Assigning these characteristics to colours becomes problematic if we are trying to have an even spread - for example, a lot of the top tier characters (eg. Thor, Iron Man, Sentry), have a high share of the “better” abilities.
The bulk of numbers appearing together is throwing me off when it comes to assigning colours. I had dabbled with colours in my various classifications but it was just too complicated.
Thus, in my most recent one, I took a more meta approach whereby the characteristics are seen through the representation of health, healing, Team-Up gain, tile damage, bonuses in addition to single hit damage and the cost to use AP abilities (these have already changed, so are not final). This approach allows the character colours to matter far less.
Perhaps there is a sort of middle ground here, with characters first formed on some of their broader features and then ingame damage and abilites influenced by this and using your 7 colour concept. The alternative is to use some of the categories in their meta way and then some to make the colour categories. Maybe we could initiate a discussion about each element and come to an agreement. A classification within a classification, if you will.