Cal looks incredulous to say the least.
"Uh, so you're threatening to shoot her because her magic fire happens to be black? Did it ever occur to you that maybe someone capable of producing fire from nowhere could change its color without being hellish? Not one more step! You got a problem, you can talk about it, but you do NOT shoot people when I'm around."
Admittedly, pyromancy is such a stretch to him that changing its color seems like nothing. Which in a way it is.