Needle Ingection Question

For one part of my movie, the characters take an injection of megahyperfeurtic fluid “streangth fluid,” and i want it to look as if it is getting into their blood stream, changing the color of the skin as it goes from the arm to the hand to the shoulder to the chest and head, where it eventually dissipates. I know how to do this so it all happens at once, but I dont want that. Allrighty then!

You could try a Blend texture mapped to an Empty Object. Use an Ipo to scale the empty over time.