Add pigment to resin as needed to get the desired color and opacity.
Opacity depends on the pigment color and solids loading as well as the laminate or coating thickness. Generally opacity begins to develop around 3% in thin coatings (around .006"), but may require significantly more than 3% depending on substrate and solids content in pigment.
Red tends to have a good solids content and opacity can usually be obtained between 3-6%, this is a nice candy apple red color. Does not work well as a transparent tint.