I donβt think you can, they seem to be tied to the color that the combination of manufacturers / phones decided to use.
So, for example, I have three WP7 devices, two on Verizon (both HTC Trophy), and one on AT & T (Samsung Focus). Metro tiles on Verizon phones are red, I assume they match the red Verizon logo, and therefore the dots are red. The AT & T phone tiles are blue, I guess they match the blue AT & T logo and therefore the dots will be blue.
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