So I have a single 4 wire humbucker pickup (an old Strings & Things) and I don't know the color code.
I have it wired as illustrated and the parallel is fine, no noise, but in series is noisy and I'm assuming out of phase.
What wire(s) do I need to change to get the series setting "in phase?"
What makes you think you have it wired in series if you don't even know what wires are what? You need at least a meter to find out which wires go to which coil. That a beginning. Then you need to find which wires are the "start" wire of each coil and which wires are the "finish" wires.