changing viewer background color in FCPx

You have something in your timeline, that, from what I can see of the thumbnails, is... black!

Move the playhead to an empty area of your timeline, and you should see that indeed the background IS white.

We all understood that you wanted the Viewer background to be white.

Here is a viewer in black - notice that, as Larrie pointed out, that ONLY the area of the actual movie is in black, and the surrounding space is a dark grey:

Now here's the same viewer in white:

The point is that, if you have a clip that fills the frame, there is no background to paint white (or black):

But if you scale, or rotate the clip, you will see that the background is indeed white:

I just went through this same thing. I hardly ever change the background color and had to remember how it worked. The player background color only changes the color of the background behind the clip in the viewer. Not the black area around the clip. This is useful if you are rotating a clip or enlarging a smaller aspect ratio clip to see if it fills the frame. You can test it by inserting a gap clip into the timeline and playing it.

In a graphics app like Photoshop or Pixelmator Pro you can create a 16X9 frame to use as a guideline - a thin border of white (or the color of your choice) over a transparent background:

Save that as a PNG somewhere. In FCP you can bring that in to the application as a Custom Overlay via the View Menu:

Then choose that imported image as a Custom Overlay:

You can vary the opacity so the guide displays as you prefer:

And now you have a guide box only visible in the Canvas, that overlays for display purposes above all your work and can be turned on or off as needed:

MtD

I think this can be useful: if you are scaling or rotating a clip and want a better idea of what sits inside or outside the frame, you can click the button marked with an arrow in the picture below. It will make it easier to discern the area outside, and also let you see the parts of the clip that get out of the frame. Notice there is a faint square pattern in the area around the frame:

And here is what you see for part of a clip that gets outside the frame:

I am talking about the black space behind the playback popup box and above the timeline

Please clarify the identity of the clip you are inserting into the timeline. Generator? picture?

Please take a screenshot with shift+⌘3 without cropping it.