I would be incline to paint it in the green taken from the colour of the leadlight this will make a feature of your front door but at the same time won't detract from the leadlight or as others have suggested a brick red to complement the brickwork.

sadly just found out we cant use the copper paint for external door use :( but have found this colour which is close to the copper. Thoughts? thanks :)

I just looked on the Dulux charts , and colours like Strong Strawberry or Rusted Crimson are earthy but have that reddish/burgundy vibe , and would blend in but still brighten the entrance . The other option would be a real bright red to really lift the space and add the Wow , although as it seems it isn't seen from the street , it probably won't schieve much , so more toned down earthy burgundy reds may be the go .

Post a picture for more comments. Otherwise be bold and choose your favourite colour.