Out of the box, SOLIDWORKS has default settings for the Background appearance. If you go to Tools, Options and System options, click on Colors. You will notice the "Use document scene background" is checked and recommended.
However, some people are sensitive to light or the brightness of the screen. You can change the Background appearance of your graphics area to your likings. Go back to the Colors tab and choose between:
1) Plain (Viewport Background color above)
2) Gradient (Top/Bottom Gradient colors above)
3) Image file and choose an image you prefer.
After making your selection, choose the color or colors by clicking the Edit button.
Or, if you are going to use an image, browse to the image you prefer.