That is a good point but perhaps a good answer is that they could do like they did with potential and make all players who existed before "Chemestry" is introduced have say a "Grey" or neutral personality.
Going on the colours idea you could have a stack of personality types and potential mixes on the floor at any one time although remembering that there are a maximum of 5 players out there at any time does create some sort of cap.
Off the top of my head with 0 thought
Red = aggressive, tough guys who don't back down. Like other red guys. Don't like blue.
Blue = sportsman-like guys they are very fair and friendly and like to see everyone happy. Don't like red.
Silver = ball hungry guys, they like to score a lot more than they like to pass or defend. More than one on court at a time is trouble.
Pink = demure guys who like to be a member of a supporting cast. Go well with Silver or Green.
Purple = leaders and role models. Hard workers who want the team to do well. Like Red and Gold. Only one on at a time is best.
Gold = win no matter what guys who go for gold. Dislike Blue and Pink, like Silver and Purple.
Green = envious guys, they don't like players that are better than them and are happy if they are the best on a bad team. Really like Pink.
Grey = neutral, no-one likes or dislikes them and they don't like or dislike anyone - all older than the system players.
Ideally there would be no one "best" combination but many workable ones which may give you a small bonus in your games of maybe 1-5% for example good combos would be:
5 blue
3 pink, a green and a silver
2 red, 2 gold and a purple
Bad combos that give you a small penalty of maybe 1-10% would include
2 purple, 2 silver and a green
2 blue, 2 red and a gold
5 green
I am sure this could easily be bettered.