Colorista + Filming white paper
 

When filming with the 1Dm4 I usually try to set a white balance with Kelvin. However, depending on the lighting, and how much time I have, it's sometimes off. Would putting a piece of white paper in front of the lens for a few seconds in that light, then using Colorista's white balance dropper be a good way to get the right colors?

This website might help. You might consider purchasing their "Warm Cards" which will give you complete control over white balance in most every situation. I use them, and use the blue cards for most interior interviews.
Vortex Media: VIDEO & PHOTO Tools and Training

The only question about white paper is: is it truly white?
A greycard might be a solution, but check the mentioned link!