To unlock the two alternate ship skins for the fury version of all the craft you must complete the following.

Skin	How to unlock
AG Systems Zone Battle Skin	Unlock Turbulence Campaign.
Assegai Zone Battle Skin	Unlock Nuked Campaign.
Auricom Zone Battle Skin	Unlock all Aftermath Events.
EG-X Zone Battle Ship Skin	Unlock Corruption Campaign.
Feiser Zone Skin	Unlock the Impact Campaign.
Goteki 45 Zone Battle Ship Skin	Unlock Vortex Campaign.
Harimau Zone Battle Skin	Unlock Aftermath Campaign.
Icaras Zone Battle Skin	Unlock all Aftermath Events.
Mirage Zone Battle Skin	Unlock Nuked Campaign.
Piranha Zone Skin	Unlock the Voltage Campaign.
Qirex Zone Skin	Unlock the Voltage Campaign.
Silver Fury Skin (All Fury Ships)	Medal in all campaign events.
Triakis Zone Battle Ship Skin	Unlock Vortex Campaign.