How to use it
Apply a gradient to a border.
When to use it
If you've got an otherwise simple design, and you want to use brand colours to highlight an element, you could put a border around it and apply a multi-colour gradient to the border. This is good for grabbing attention.
What to watch out for
If you've got lots of other colour happening in the design, this can look over-the-top. If your element (The circle below, for example) has a fill, a colour gradient becomes much harder to do well.