The design may look more interesting if the sleeve was a combination of the end pieces of the upper far left, the whirls from the top 3rd, and the shoulder area from the 2nd and 3rd upper from the first post. The tags on the end of the sleeve suggest the arm is being sealed. Is there a story element to the arm? Just a design you liked?
You are doing well with color combinations already. It depends on what the story of your character is. Is this priestess evil? Most people would say to throw red, orange, black, or violet on her. No backstory? It is all up to you. Just understand complimentary colors and which colors clash together and decide what you want. The rest depends on which colors you want to show the most and whether or not a color is making design detail difficult to understand.