Here is a Youtube Channel Art Template I created in Photoshop to help you design better channel art for your YouTube Channel. It has been custom designed to point out the areas you need to be aware of while designing and the important information you need in order to make you more Subscribable.
These are the Blue boxes for the use with blue items
These are the Red boxes for the use with blue items
These are the Green boxes you've always wanted
These are not the Black boxes you are looking for.