Very simple. A user is moving a mouse over a web page. Every element the mouse moves over receives a highlight as the mouse touches it, and the highlight is not there when the mouse is not touching it. Therefore only one element receives a highlight at any point in time. If any other elements have a highlight they receive at most 1/n strength of the highlight (where n is the number of other elements, besides the main tracked one, that received this highlight). This condition means that, effectively, the highlight is only for 1 area at a time.
Let's be as efficient as possible. As visually attention grabbing as possible, without being jarring. And hopefully as aesthetically pleasing as possible.
I thought about some options, but unless people demand I won't bore you with those. I'm not a UX guy but kind of wish I was since I am interested in how to make this UX the best, most helpful possible.