I notice the legend here, but it shows in a light color (too light to be reasonable). I think this should be improved in the example.
But maybe you had a trouble displaying tooltip because you are on a hybrid touch-and-pointer device? (for example a laptop with touch screen)? If that's the case, let us know!
We have just removed the code forcing white background from the examples so that the displayed tooltips uses 100% theme-provided colors. By chance, the Gray and Triton themes have a "darker" tint on the tooltips. They can easily be overridden by setting the StyleSpec setting to the tooltip component.