Hue-controllable RGB LED lamp

I've got a question about the 'sinking' technique:
When the source is +5V, and the PWM pin is HIGH, no electricity will flow even if the +5V is capable of higher current than the pin, correct?

Also, how much current can an arduino pin safely sink? I know the pins can source 40ma, but didnt see a value for sink.

Thanks, and very nice code!