Nice!
For the light blue tile, I would say just not being able to go would be enough. If you are afraid the player could not understand why, my suggestion would be you play the animation of getting merge, have the big dark blue box appearing and disappearing right away to get back to the previous situation with one move lost (the contrast of color is explicit enough) :)
The "it launches you somewhere" would add another dimension to the game, you can do something with it but it would be a new gameplay component (not a bad one if well made though). Jumping over holes, having a third dimension... your choice :)
I will check it from time to time to see the new updates then!