Feature: Option to add background color to help page

[FrostyNick]

Having a default background to the help page would be a nice addition and might be helpful for new users that can't see anything with a very white image in some cases. With the default text color ( #fff ), it's also harder to see what's behind the text. I didn't see a way to change this with just the config file.

Using swayimg version 3.2.

Screenshot example with modified config