Creating a custom dotted line border, where I can change the colors

Hi all, 

I'm trying to recreate a dotted line much like the one here. Basically I am trying to get every 5th dot to be a different color. 

I tried to create it by making my own brush but then the dots just begin to warp. See below. Any tips on getting a uniform, not warped dotted line brush to work?

This is the pattern I want to work from.

tried to make it a brush here, seems like it would work. 

and then things like this happen. 

 (dots aren't perfect circles anymore)

I also tried to make a simple dotted line brush wihtout changing colors, but even if I want to expand the line and go in and change every 5th dot myself, I cannot singularly select the dot I want to change the color to.