Color different for the current category

By default it will add current-cat class to the current category item.

If we need to change that, we can use:

‘current_category’

(int|array) ID of category, or array of IDs of
categories, that should get the 'current-cat' class. Default 0.

as mentioned in the dev docs for wp_list_categories() arguments:

Then we can style it as needed via CSS.

Example

For your setup:

.ul-cat .current-cat a {
     color: #aaa;
}