Trying to make an animated gif but it only shows one color

Your Photoshop document is zoomed to 8.3%. The save for web dialogue preview is zoomed to 100% so showing only a fraction of your document - hence why you are seeing only a section of one colour.

As an aside 5000px x 5000px is very large for a web document (as mentioned by JJMack above)

Dave

Instead of posting your animation as a still Jpeg image.  Can you save it as a PSD and upload the PSD and post a link to it so we can see what you did in its time line? Your Jpeg has color ob your screen. In your Save for web dialog you may want to view the imags so it fits into the preview window you may have a larger frame size you have view 100% change it to fit..  Where you are viewing you frame zooned to 8.33% in photoshop. You should not for web size animations have that large of a frame size..