Aurora is an addon which restyles the default Blizzard interface to a clean, minimalistic theme which is consistent across the entire UI.
A lot of time has been spent on not only basic development and updates, but also refining and perfecting the appearance of each window and every frame.
A single colour, that either matches your current class or is a colour of your choosing, is used for highlights and emphasis.
Open the Aurora options from the in-game addon options, or type /aurora.
Please report all issues on GitHub.