When I am not sure about a color to border a quilt with. I go to my fabrics and pull out many different ones that I can audition with my blocks on the design wall. I unroll it and let it hang next to them for a while. Some are," Oh my gosh, no! But, make sure it is a "That's perfect!", in your mind before you settle for less. This gives me a much better idea of what the colors will do with my blocks. I have been surprised many times what looks the best.
If you don't have the right one... Take it to the quilt or fabric store with you. I hope this helps.