The 1989 Phthon Viper came with a black version of the rifle, and there was a dark/charcoal gray version that was released with the Battle Gear Accessory Pack #5.
When in doubt check YoJoe.com
"Vipers! They're always fun!"
"There's only two ways out of my command: On your feet like a man, or in a ditty bag... An itty-bitty ditty bag!"