here is more on this substance from wikipedia:

The color of its aqueous solution varies from green to orange as a function of the way it is observed: by reflection or by transmission, as can be noticed in bubble levels, for example; in which fluorescein is added as a colorant to the alcohol filling the tube in order to increase the visibility of the air bubble contained within (thus enhancing the precision of the instrument). More concentrated solutions of fluorescein can even appear red.

apperently it is also used in photography:

Ophthalmic photography has at times seemed almost synonymous with fluorescein angiography. Since its introduction in the early 1960’s, fluorescein angiography has become an essential tool in the understanding, diagnosis and treatment of retinal disorders. This diagnostic procedure utilizes a specialized fundus camera or scanning laser ophthalmoscope to capture rapid-sequence photographs of the retina following an intravenous injection of fluorescein sodium. Photographic or video images taken as the dye courses through the eye can demonstrate abnormalities within the neurosensory retina, pigment epithelium, sclera, choroid, and optic nerve, providing clinically useful information for nearly the entire spectrum of posterior segment disorders.

We hope you enjoy this fun video

thanks to opsweb for the great info