Most blocks can be customized in the Block Settings > Appearance. You can choose from white, back, and gray background colors. But you can easily change the block background to fill it with a specific color other than those provided in the Block Settings.
Changing the background color
To set a plain color as a block background, follow these steps:
1. Use an image editor to create a rectangle shape filled with the color of your choice. Alternatively, search online for "color swatches" and take a partial screenshot of the color you like.
2. Upload this piece of the color image as a block background using the steps outlined in this tutorial. Result: