Not just close, BS381C:627 was the incorporation into 381C of the colour chosen from BS2660 (Fore runner of BS4800). When the RAF needed a polyurethane colour for the underside of it's jets in the 60s (as there wasn't an aluminium PU paint at that time) a colour was chosen from the 'generic' colour chart which was the closest to the shade & hue of aluminium/high speed silver.
Same, as John says, with Barley/Camouflage Grey, hemp/Camouflage beige and a few other colours.
Dug this up whilst doing some research into Hunter undersides.