Laws regarding vehicle lighting vary state-by-state. In Michigan, the law allows either red or amber brake lights...but it does not mention both, so an officer might interpret that to prohibit the combination. At very least it is unusual. That alone would keep me from doing it...I would not want to confuse the drivers behind me. Using red bulbs or LEDs would be an option, though.
You would need the trailer to be wired with 5-wires to have separate amber turn signals, and you would have to rewire the brakes. Some, if not all the 2010 trailers are 6-wire. The 2011 trailers are 4-wire. The 4-wire version continues with four wires all the way to the trailer connector, where it hooks to the 7-wire Spyder connector. You would have to modify the connector and separate the brake and turn signal wires if you changed the wiring. The brake and turn wires are apparently hooked together in the connector, with diodes to prevent backfeeding. I have not visually verified this yet, but that is how the wiring rings out.