Not really. The spell description says it can color things, then specifically says that this is a temporary effect. To use it to color something but say it's really "soiling" seems like stretching the rules.
Note that soiling doesn't go away automatically, but it's not really "permanent." This is an effect that Mage: The Awakening would call "lasting." The dirt sticks around after an hour, but you could still clean it mundanely.
If I were your GM, I'd let you "soil" it with soot, as if the blade had been held over a flame. It could pass as a black-colored blade, but the DC to notice would be much lower than if the blade were actually colored with stain or due to its substance. Additionally, any rubbing or cleaning would have a chance or revealing the deception.
Note that you could do this soiling mundanely and save the spell slot.