Changing "Contain for Large Image" background

Hi,

Just bought the Easy Slider Pro, and it works like a charm.

I just need to do one small change, and that is to change the background color of the Image fill mode, I what it to be white when I use “Contain for Large Image”, and not black.

How do I do this?

https://ww.wp.xz.cn/plugins/image-slider-widget/