I use their olive green, but some say it should be green ochre. However, the olive green looks closer to the photos of restored guns on the battlefield I have seen. I understand that a four gun  battery of Confederate 6pdrs at First Manassas, named after the apostles, had red carriages. To quote Paul Stevenson in Wargaming in History: The American Civil War (Argus Books 1990), "Carriages, caissons, limbers and wagons were 'olive green' in the Union army (i.e. really a shade more like yellow ochre) and grey blue in the Army of Northern Virginia." I honestly think the Vallejo colour that most suits his description is actually green ochre, and for the Confederate guns Vallejo grey blue should work (but of course many Confederate guns were captured Union pieces and may well have been left olive green - likewise captured wagons, etc.).

I as going to say 'olive green', but the answer above somewhat puts that in the shade!

Yep, olive green would be my choice as well. Every cannon on display at Gettysburg is olive green, so make of it what you will...

regards, Bill