Hi there,
you will need some CSS.
This for example:
.left-sidebar .widget:nth-of-type(2) {
background-color: #f00;
}
The nth-of-type(2) property will target the 2nd .widget in the left-sidebar
You can repeat that CSS rule and change the 2 for anyone you like.
And if you want to use one of your Customizer GLobal Colors then you can use a var like so:
.left-sidebar .widget:nth-of-type(2) {
background-color: var(--contrast);
}
Just swap the --contrast for your chosen global color variable name