You can make it grayscale, but having color then introduced into that grayscale is not possible (at least I do not think it is with Movie Edit Pro)... unless you exported each frame individually and colored each then re-assembled them... since there are 29.97 frames per second in North American video, that would be a lot of editing.

To make the video grayscale in Movie Edit Pro 14, open the video in time line mode, right click on the video and choose video effects, then when that opens (separate graphic) there is an area in the middle right side that says color controls. If you press that button, then move the second slider to the left, press ok. That is all you need to do to make it grayscale.