I would question my own memory, but I took notes.
For Wintersday, I transmuted my regular armor into festive gear (Warlord's Crown to Festive Hood, Warlord's Raiment to Festive Sweater, Elegy Breeches to Spearmarshal Pants). In preparation I took notes on the gear used and the dyes used. I clearly had four dyes selected for hat and legs (hat: Sunfire Lava, Cocoa, Blue Steel, Flare; legs: Sour Apple, Sunfire Lava, Molten, Shadow Orange) and now only have three options after transmuting them back. The underlying items pre any transmutes are Light Dragonscale Headdress and Bladed Pants.
The wiki doesn't list the number of dye channels there should be.
A screenshot of them with three dyes, leaving out the Blue Steel and Shadow Orange.
Am I crazy? Did I somehow think I had four channels before when I didn't? I swear I wrote down the dyes directly from the screen before swapping to festive stuff.