My current preferred method of developing and testing ideas for interfaces I'm designing is creating interactive, sketchy, grayscale prototypes using Axure. I find using grayscale helps put the focus on the interactions rather than the design and the sketchy style stresses the unfinished and disposable nature of a prototype.
I've had success with this method within my team and with user testing but sometimes find it hard to 'sell' stakeholders on the ideas using the same prototypes. Has anyone else experienced this, how did you overcome it?