I posted to this question because it was helpful to see the formula for that assigned 2 colors to a task with 2 resources. Thank you!

Now here is my question - does anyone have a formula that will allow multiple different resources to be assigned to a single task but display the color (via flag) for the resource with the greatest % allocated? I am using Project 2010 & when I assign more than one resource the flag stops working.

Unfortunately, no. The formula works on a task field [Resource Name]. Assignment units is not a task value, but an assignment value.