Custom Color Editor uses the well known Hollow Knight mod Custom Knight, so if you want to use HKCCE, you must have Custom Knight, or another custom skin mod. If you want to know how to get custom knight, then watch this video.
keep in mind, that when you download the custom cloak zip file, you need to extract it and put it inside the Custom Knight folder.

if you need more information, or want to suggest something, join the discord