Rods are highly sensitive to light and let us see under a low level of illumination. Cones let us see colour, but need more light to function. The colours we see in objects are those that best set them off from their background. Choose colours in context, not in isolation. For the background use a muted, light, colour such as pale grey or blue.
Colour vision depends on the outputs of the different cones.
These are coded as difference signals. One colour difference signal is red versus green - the red and green cone outputs are weighed up and the resulting signal depends on their relative strength. The second colour difference signal is yellow v blue - which uses the red and green to deduce yellow. A third signal uses all 3 cones to produce luminance. They analyse the picture into 3 basic colour components but then transmit the information as 2 colour difference and a luminance signal.