well, in general, you should have right, left, and mic, with a ground for each on the iphone end, and all 3 will have a common ground. for the headphones, right and left, with a ground for each, and ground is shared.
you will want to remove the protective coating with a microtorch or other heat source, solder and heatshrink, as opposed to twist together. You will also want to look up the pinout for the iphone side of it, and use a continuity tester to identify what each cable usually is.
red is USUALLY right, blue or green is is usually left - the white on the sennheiser is unusual (i double check this either by following the cable to the end, or using a temporary connection with crocodile clips between a prepared, tinned end of the headphone cable and jack).
Red to red, white to green, and 'copper' to 'copper' should do the trick. all 3 have the pesky coating, so you'll need to remove it.
this is the exact process/tools that have worked for me in the past - but instead of the jack, tin both ends, press to check, then solder.
The yellow/green is earth. It is required for safety but not for powering up the display.
If there are no metal parts exposed (and some other requirements) this wire might not be required.
The orientation of the other two wires does not really matter for getting things to work. The live wires are brown = black and the neutrals are blue = white.
Best Answer
In short, capacitance between the two wires is your answer.
Here's an example I faced many years ago. A friend of mine rewired his house but asked to borrow my meter before he connected ground to the pipes coming into the property. He phoned me up and said there was 115VAC measured on the unconnected earth wire and he was frightened of grounding it. (Local AC voltage was 230V and I assured him that "live" was at 230V, neutral at "0V" and the middle unconnected wire would find a voltage that was roughly halfway between the two wires (due to capacitance between conductors). He connected the earth wire and no problems.
What you are seeing is the natural effect of capacitance coupling the voltage on one wire to another in close proximity.