Opaque Liquids are impenetrable by light and are best measured using Directional 45/0° reflectance geometry. This is the geometry that most closely matches how the human eye 'sees' colour.
Translucent Liquids allow light to pass through, but only diffusely, so that objects on the other side cannot be clearly distinguished. Both reflective and transmittance measurement modes may work well depending on the translucency of the sample.
Transparent Liquids allow light to pass through with little or no interruption or distortion so that objects on the other side can be clearly seen. These liquids can only be measured using transmission instrumentation.
Resins are the components of a liquid that will set into a hard lacquer or enamel-like finish such as automotive paints, nail polish and epoxy resin. Resins can be organic, derived from plants such as coniferous trees, and can also be synthetic such as liquid monomers of thermosetting plastics that are not derive from plants.
Resins can be transparent to opaque, and so can benefit from wither transmittance or reflectance measurement modes depending on the opaqueness of the resin. If you are measuring both opaque and translucent/transparent samples, you may prefer to select an instrument that measures in both transmittance and reflectance mode.