Why don't you post your question on the California Forum?

Maybe Polka dot plant for the dark understory plant (sorry, the botanical name escapes me at the moment), but it comes with pink/red and also white/green. You could use the dark variegated tradescantia, but it can be invasive. Both like a bit of shade, so you should get your taller plants going first to provide the shade. Ponytail fern (asparagus 'Meyers') is a nice lime green and will take a bit of sun.
Plectranthus varieties are another good one with diffent foliage types.
Loropetalum 'Plum Delight' might be something you'd like.

Cannas have some lovely foliage, but they also get tall unless you can find a dwarf variety. Cleopatra is one of my favorites, also Tropicana.

Tall and leafy....maybe Azara dentata or microphylla.

crotons
Ti plants