I found out how to mod avatar skins using a flash drive. + Rep if my tutorial helped you.
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What your gonna need :
1. USB Xplorer
2. Horizon

So 1st get your profile off your USB by using USB Xplorer.
Now, open Horizon and go to "Profile Mods"
Then, choose "Avatar Color Modder"
Choose "Open Profile" and choose your profile that you saved.
Now customize the colors you want and click "save" when you're done.
It will rehash and resign so you dont need Modio.
Now go back to USB Xplorer. It should still be opened. Delete your profile and replace it with the one that is on the desktop. It looks the same but it is modded.
Now go on your xbox 360 and put your profile back on and have fun!!

UPDATE: If this helped you, please give + rep and say Thank You for this topic.