Sometimes in direct sunlight (which contains UV light), if the fluorescence is strong enough you might be able to see an "overblue" effect - kind of a blue "aura/glow" which can sometimes confer a milky or oily look to the stone - not a common effect, however.
Pyramid
Try this one
Take the diamond to a sun lit window, hold the diamond in the sunrays to absorb the UV then rock the stone from side to side evoking a scintillation effect. You can often see a distinct blue flash from the reflected light.