sidebar background color

Depends on which sidebar? 🙂

You will have to create custom CSS to do this, so if you are using jetpack, you can use its Edit CSS feature, otherwise if you are not using this, get a plugin like Simple Custom CSS.

You can do something like this example:

#right-wrapper {
    background-color: #ccc;
    padding: 12px;
}

Basically, you would copy and paste that into your custom css stylesheet (with your colour and padding choice of course).

Please note though that this will not create a full height column background if your content area is longer than the sidebar content.