I could recreate my player sprites and recolor them by hand (would be nice if you could paint bucket across all animations, but oh well) but this is a pain in the butt, doesn't let me change colours easily later on, and becomes a massive amount of work if later on I want to add more colour modes.
There's a very quick way to add new skins using the Desktop Download version of C3
USING THE DESKTOP VERSION:
1. Create Master Spritesheet of all character animations
2. Split the Master Spreadsheet into separate files using a spritesheet splitter tool online
3. Put the split frames into a single folder called "Import" or something
4. Load the frames into a Sprite Object and get it set up how you like (In your case just replace the old frames with these new frames)
Adding new skins:
1. Edit the original Master Spritesheet to a new color using global paint bucket
2. Split this new spritesheet the same way you split the Master Spritesheet
3. Put the folder containing the new frames in the same location as the "Import" folder. Rename the old "Import" folder to something else, and rename the new folder with the new skin to "Import"
3. Duplicate the Sprite object you'd like to add a new skin color to
4. There's a button in C3 Desktop version when you're editing a Sprite's animations called "Reload from source" or something. This will re-fetch the files from your computer using the file locations. So it'll find C// Desktop/import and replace all your frames in the Sprite Object with whatever it finds, in the proper order.
This takes a bit of setup but once you get it going it's very fast. I had a Sprite with over 100 unique frames and 30 separate animations, and this allowed me to add new skin colors within a few minutes