selective coloring is not very popular. In addition, my black and white looks rather grayscale, I tried for a sharp B and W. I know it doesn't meet the rule of thirds, but the way the flower and the lake are framed by the mountains seemed to over-rule that rule, LOL.
You do need quite a bit more contrast in the B&W portion. As you eluded to, you have no real blacks or whites in the shot.
Also (IMHO) the amount of selective coloring you provided doesn't do anything--except leave me wanting more. I don't see what feeling, message, emotion, etc., you wanted to convey (if any).
The composition is fine. The rule of thirds is more like a guidline rather than a hard and fast rule.