Colored Planks are decorational blocks added by Engineer's Toolbox. They are purely decorational.
To obtain Colored Planks, the player must use Spray Paint. Right-clicking a Plank will color it the corresponding color of the Spray Paint. Any Plank will do, as long as it is properly registered in the Ore Dictionary. Colored Planks cannot be restored to normal Planks, but they can be used in crafting recipes with normal Planks since they are registered in the Ore Dictionary themselves (this also means Colored Planks can be re-sprayed a different color).