The Gray Death Legion has always painted its ‘Mechs gray, usually opting for a gray-on-gray camouflage.

Per FM:Mercenaries, page 56.

Other references:
Wolfhound, FM: Mercenaries (plate 14)
Shadow Hawk, CM: Mercenaries (p 105)
Banshee, CM: Mercenaries (p 109)


Insignia:

The Legion’s trademark gray skull insignia is set over a red crest and emblazoned on the left shoulder of unit ‘Mechs. A colored circle painted on the lower right leg identifies the battalion; yellow for first battalion, green for second, blue for third, and red for the Headquarters Company and regimental command lance. On the right shoulder, a warrior may paint a special unit crest (usually a company insignia). The two command units wear the Legion insignia on both shoulders.

 

Per FM:Mercenaries, page 56.