This is not just the colour palette, this is a vast amount of the head, as well as colouring. You took some of their colours as well as some of their design and shading. Even if you add something new, does not automatically mean you can just neglect the parts directly taken from a different skin. If you're large enough to admit some of the colours aren't yours and seeing as the head is largely not yours as well, credit at the very least is due.

This in fact breaks the rules. Seeing as you must have permission to use parts (in fact directly taking is always disallowed according to the rules). The very least you can do is to mention his stuff.