I've seen dark green lamp cord before...probably on ebay. Not the same color but, it would look nicer than black or brown...as long as the greens don't clash. And dark green extension cords too...in all different gauges.
There is a website that sells vintage looking wire also. Just google vintage electrical parts...I think that's how I found it.
A cord from an old appliance isn't a bad idea at all, in my opinion. I wouldn't have a problem using it as long as it was supple with no cracks or stickiness. Most old sewing machine wiring had rubber insulation & rubber deteriorates. A lot of appliance wiring that's a little newer has vinyl insulation that lasts MUCH longer. I know I've got extension cords & small appliances with cords from 1965 (year I got married) that are still in perfect condition...just depends on what they're insulated with.