Cut a swatch of gel for every folder. The gel is on a white background beside the clearly
typed number. All drawers are separated by brand (and size?). It makes it very easy to get
in there and find a color, especially as a designer when you are just looking for something
last minute to match or fit in with a palette.
I use a fine sharpie with just the number in each corner (readable in lower right hand
corner no matter what side you're holding), while I find that many theaters I've toured to
use china markers, and only mark once. On the rare occasion that I mix my gel with
house gel in a rig, it's easy to see which ones are mine.