Would it be feasible in any rocket engine (liquid or solid) to add one of the following elements: barium, lithium, sodium, copper, or calcium to create different colors in the exhaust plume, or would those elements render all engines not flight worthy?

Would it be feasible in any rocket engine (liquid or solid) intended for flight above the atmosphere to add one of the following elements: barium, lithium, sodium, copper, or calcium to create different colors in the exhaust plume, or would those elements render all engines not flight worthy?