Puzzle 300: Not Alone Loop

This is a new type, and the first puzzle of this type.
Rules: Draw a single closed loop that passes through every cell horizontally or vertically, and does not cross itself. The loop must make a 90 degree turn in every circle. No two circles of the same colour may sandwich a circle of the opposite color. in other words, the loop may not visit two white/black circles immediately before and after visiting a black/white circle.