My current 135 is LeMans Blue and I love it. It is definately "blue" with no hint of any other color in it. Under certain lighting conditions you'd be hard pressed to tell the two apart. But, as was stated above, the IB and some sun bring out much more color play and interest. Plus....it's M specific. Negative...a slight purplish tinge once in awhile, again dependent upon the light.
If IB and LeMans were both offered on the 135, I would have ended up with the LeMans despite the exclusivity of IB.
Go with your heart. I've made 5 (yes 5) color changes over the past year while putting together my individual order for the new car which'll be ordered next week. And I'm ending up with what I sort of started with. What an idiot I am. But very happy now
Hope that helps - Mark