In poker tournaments, the term “color up” describes an activity during which certain smaller denomination chips are removed from play and replaced with larger denomination chips.
For instance, once a tournament reaches a 5,000/10,000 level and no future levels require 100 denomination chips, these chips will be removed (usually during a break), and players will receive the amount they had in larger chips. So, if you have 2,000 worth of 100 chips, these will be removed and replaced with two 1,000 denomination chips.
Coloring up is done in tournaments to facilitate play and reduce clutter. It helps keep stacks manageable and makes it much easier to keep track of players’ chip counts as the tournament progresses.