More Science
Many highlighters fluoresce or absorb and emit light, which makes them glow in the dark. But why? Light is a spectrum. The region of spectrum that we can see is called visible light. It ranges from red to violet light. However, there are other types of light, including infrared and ultraviolet (or UV) light. UV light is what a blacklight bulb emits. More specifically, it is UV-A light, the long wavelength region of UV light.
The ink of the highlighter pen show a unusual glow becuse it converts some of the incident ultraviolet light that is invisible to humans into visible light.
White light is a combination of lights with different wavelengths. It contains a very small portion of UV-A light also. When you colored the tape with blue and purple markers, you created a filter that blocked out all colors of visible light except blue and purple. It is enough to make the highlighter fluoresce because the wavelengths of purple and blue light are close enough to the UV spectrum.
