There are many, many ways to emulate wooden decks. For planks to be different in color, here is a nice article on how to do it. The resulting decks are amazing, although work, put in there, is huge. :) Don't forget, that planks should vary in color very little, and don't overdo it!
I've accepted that technique once, and I, indeed, overdid color variations, even though I hadn't thought about it this way then. :) Deck will look like a patchwork of different types of wood, which it wasn't usually.
Other techniques can include, for example, drybrushing planks with different colors, using oils (my favorite) of different colors, but it's much harder than drybrushing... Experiment. :)