My initial problem seems to be irrelevant. I did not understand what was meant by "throttle" which is more of an RC jargon misunderstanding than it is an issue with raspberry pi. (If you're looking for an answer this link shows it pretty well.)
Sorry for being off-topic! Sometimes it's hard to know when you are working from little experience. :)
Presumably you have a common anode RGB LED. In these you connect 3V3 to the common anode and connect each leg via a resistor to a GPIO. Current flows when the GPIO is set to 0V and acts as a current sink.
Contrast with a common cathode RGB LED. In these you connect ground to the common cathode and connect each leg via a resistor to a GPIO. Current flows ...