Edd check out euporbia Polychroma. This is a neat non invasive plant producing....now starting.....wonderful mounds of acid yellow/green flowers. Ok, it doesn't fit your criteria of being free but I would hesitate to plant invasive stuff.
From green to blue how about elymus magellanicus a glaucous evergreen grass. More blue than green in sun and vice versa in shadier spots. The pinks have a similar colour foliage in flowers from white to red to purple.
If in doubt simply do not plant anything remotely invasive