I know there has been a lot of debate about the aesthetics of this model on forums, personally the in game effects of a model have to be balanced against their design if you play regularly. I have become an infrequent player at best, so it's all about aesthetics and what's cool for me.
I chose to build my Land Speeder kit as a Vengeance for one reason - plasma weaponry. The heavy plasma cannon on the Land Speeder Vengeance was a no brainer for me.
To keep the same color pallete throughout the army, I kept the weapons gold, and made the broad surfaces dark green, and the Exterior surfaces black.
The silver was paintd with Ironhull, Argax Earthshade and Chainmail. The window was painted with Fenris grey. I opted not to free hand any Disciples of Caliban symbols for now.
