It has a specific meaning in Optics, the study of lenses, filters, light and color.
The official definition, that applies to dichroic glass (not dichroic filters, which is related) is The original meaning of dichroic, from the Greek dikhroos, two-coloured, refers to any optical device which can split a beam of light into two beams with differing wavelengths. Such devices include mirrors and filters, usually treated with optical coatings, which are designed to reflect light over a certain range of wavelengths, and transmit light which is outside that range.
I have no idea if this dildo actually does this with light. It would be cool if it did, but it would make the dildo very expensive. It is
a very expensive dildo )$157.99, I think) but I don't know what applications using real dichroic glass in a dildo would be.
I could be wrong, but in this context, I think it just means "two colors of glass."