If you want a colored inner border, I would either make it blue (the color you have the least of on the edges) or a totally different color. What is the background color of the cat fabric? If it's a darker blue or a black, maybe that. Then you can make a wider border of the blue or if you use the blue as an inner border, make a wider border of another fabric. I like a narrow (like 1" or 1.5") inner border and then a wider outer border but that's just me.