Lyric discussion by taskforce 

Cover art for Richard III lyrics by Titus Andronicus

As the entire album is supposed to be based on the US civil war, "blue trampling over grey" seems like it would be witnessing union troops 'trampling over' confederacy troops - the colours of their respective uniforms.

"green over brown" is less clear - the only thing I can I can think of is grass growing over the mud of the battlefield.

You are halfway home with the "green over brown" lyric. I think it is the grass growing over the dirt/mud/soil lying atop their graves.