I would say it depends on the nature of the intersection, but generally if the light turns red before you enter the intersection you've run a red light. If it turns red while you are in the intersection, you've run a yellow light.
For both red and yellow lights, the road rules talk about 'approaching' and when they must stop. In terms of stopping, both provisions talk about:
- If there is a stop line, as near as practicable but before the line;
- if there is a 'stop here on red signal' sign (but no stop line), as near as practicable but before the sign; or
- if there is no stop line or sign, as near as practicable but before the nearest traffic light.
I would think then that the relevant point is the entry point of the transaction, and the relevant colour is what was shown right before you did so.
It appears to be the same penalty for both infringements in any case.