The standard colour for Skyflash missiles is BCS381:627 Light Aircraft Grey (Humbrol 166, Tamiya XF-20, Xtracolor X15).
Prototype Tornado ADV carrying four Skyflash missiles.
Photo credit: MilborneOne Creative Commons Licence CC BY-SA 3.0 via Wikipedia
Skyflash missiles on display at RAF Museum Cosford. Note that these are marked with a blue band as 'drill'.