Virtually every color in Grid is customizable, with clear names and descriptions in the Theme settings.
Use the Colors portion of the Theme settings to select your colors and assign a background image.
Select your colors
The colors are organized into five categories: Background, General, Buttons, Header, and Dropdowns/Table headers.
Click on the swatch to edit the colors. A popup with a color selector will appear, which allows you to adjust and experiment with custom colors.
Assign a background image
For Background, you have the option to upload a Background image. A high-resolution image is ideal for this option since the image will be spread across a large area.