You can easily re-color your background and other block images and make them monochrome. Black and white is a good choice when the color in a photo distracts from the message you want the image to convey. Here's an excellent article on using black and white images.
Here's how to quickly make your images black and white:
1. Hover over the block where you want to re-color the image. Click on the "gear" Block settings icon.
2. Click on the Appearance tab and located the Media content settings area.
3. Check the box next to the Add B&W filter option. The image(s) will be instantly re-colored into black and white.
4. Click Save to confirm changes.
5. Once you are happy with the background image, click Publish to make changes live.