If you end up deciding to use colored cellophane and duct tape, keep in mind, that the cellophane will melt if it's placed too close to the modeling lamp as the lamp heats up during the shoot. The cellophane will be ruined and it may also damage the lamp if you're not careful. I always turn off modeling lamps after the lights' power and positions are adjusted for the shoot, so I don't have to worry about it.