Hi Kathryn,
Yes it's possible to change by adding custom css such as the following (sets it to a blue colour in the example):
.slider-banner-col {
background-color: #0066CC;
}
Assuming you're using Adaptable, you can add custom css in the settings under Appearance -> Themes -> Adaptable -> Custom CSS & Javascript
If you don't know much about CSS, it would probably be worth learning about it to understand the above.
M