Dark green hi vis

So long as you also have lights on the front and back of your bike it should be fine.

Not so much the clothing but as PP says, the lights. I go for a helmet mounted ‘flasher’ (has white at the front and red at the back) which is particularly handy approaching junctions and on roundabouts (I tend to look towards drivers heads to maximise chances of being spotted). I also have front and rear fixed to my bike, again on flash. When I drive I more easily spot flashing lights on bikes than steady beam as they stand out more. Lastly I have a flashing band around my right ankle. I do also have a reflective gillet which I wear in the dark too... the more you can do to be as visible from all angles the better. But lights are definitely the priority. Anecdotally I actually find cycling in the dark safer, drivers tend to give more space (I do mainly unlit country lanes, but also brightly lit, busy, urban). I presume it’s because I’m significantly more visible. I don’t let it lull me into a false sense of security though!! Happy peddling! I LOVE dark winter riding, it’s magical.

As long as there is reflective material on it you'll be fine.
Along with good front and back lights.