What'd you'd do is remove the CreateLastOneStandingVictoryCondition(); line above.
Then code like this: (Example, 400 colonists for player 0; Just change the 400 and 0 in the first line if you want)
Trigger population = CreateResourceTrigger(1, 1, resColonists, 400, 0, cmpGreaterEqual, "NoResponseToTrigger");
CreateVictoryCondition(1, 0, population, "Have 400 Colonists.");
You can tweak the 400 and 0 in the first line as you want, to specify the amount and player ID (0 is usually the human in a colony game), and you can tweak the text in the 2nd line if you wish.
Hope it helps!