DO MATERIALS ALWAYS HAVE THE SAME COLOUR WHETHER VIEWED BY REFLECTED LIGHT OR THROUGH TRANSMITTED LIGHT?
The answer is no. If a material reflects light, its colorwill be determined mainly by the wavelength of the radiation that it reflects to the contrary to what it absorbs. If the material transmits some light, it can be either transclucent (i.e. scattering some percentage of the light and then assuming a different wavelength) or transparent (i.e. not scattering the transmitted light). There are no conditions that would ensure that this color is the same. The perceived color is then further conditioned by the nature of the ambient illumination, and by the color properties of other objects nearby, and via other characteristics of the perceiving eye and brain.