Video clip is smaller dimensions than project. How to change the color of extra space? I may be asking the question in an unclear way, because I come from an audio and graphics background. Apologies in advance. Hope this is makes sense...

My Final Cut Pro X project is 960x720, and I'm putting a clip on top of it that's larger, but scaled down using "Spacial conform" so it fits vertically, and there are black stripes to the left and right of the clip.

The clip is a Powerpoint and it's got a white background, so I'm using "Stencil Luma" blend to put a nice animated video behind the text. The effect is nice, but the black bars to the right and left of the clip prevent the animation from showing underneath those black bars.

I simply want those black bars to go away, or become white, so that the background video won't be clipped while the front video is on the timeline. 

Solutions?
Unfortunately you can't create a project of any size. Larry Jordan posted a workaround, which doesn't solve you're problem.

There was a tutorial that showed how you can have sequence of any size in FCPX (and thus removing black bars), but I can't find it at the moment. (EDIT: I found it! Creative Cow) I remember what you need to do though:


Go to the event library and pick a clip that has the final clips' resolution.
Make a backup copy of said clip (right click, copy&amp;paste)
Right click and choose Open in timeline.
Drag another clip into the timeline. 


This creates what is called a compound clip. Compound clips can be handled like projects, but can have any frame size. A special icon in the Event Library shows you that the clip is actually a Compound Clip.
As long as there are at least two clips in the timeline, the clip's going to be a Compound. 

If you really really really rather work with a project and want to have a custom background to cover up the black bars. I suggest to drag a solid color generator from the effects/generators section underneath your Main Storyline.