lol sorry about that :-P
Maximum loyalty is 5000 per colony.
Loyalty greatly affects how much tax income you get per turn from your population.
At 0 loyalty, you get 50% of your population as tax, eg if there are 100.000 pop, you get 50.000 creds in tax per turn.
At 5000 loyalty, you get 100% of your population as tax, eg if there are 100.000 pop, you get 100.000 creds in tax per turn.
So if you are relying on taxation as primary income, loyalty is *a must*.
However, loyalty has NO EFFECT WHAT SO EVER on COMMERCIAL income, that is entirely different !