Hello @james-salisbury,

We apologize for the misunderstanding.

Now to change the color use below CSS

#main-slider.design-2 h3::after {
    background-color: #dd3333;
}

You also need to remove the CSS given below that we have provided :

#main-slider.design-2 .cycle-caption {
    background: #dd3333;
}

Hope this helps.

Best Regards!!