Will The Plastic Colours Match

Different plastic parts are often made from different plastics and even if they are the same material they are often different thicknesses and so colour matches are not guaranteed, the thicker the material the more dense the colour.

For example Fender pickguards and knobs are different materials and knobs and tips are thicker then pickup covers.  

Gibson in particular use different materials for different parts and wheras the colour of the different parts can be close they are rarely a perfect match.