App note from Holtek on using their HT66FB574/572 to develop color effect mice. Link here (PDF)

Demands from the video gaming industry for different types of gaming mouse continue to expand. Adding a large number of RGB LEDs to the mice can produce different colours and brightness changes creating a range of visual special effects. This enhances the colour and stimulating effects of gaming mice. For example, having multiple RGB LEDs to form an outer ring on a gaming mouse can produce a colour changing waterflow effect. These are known as colour effect USB mice.