I sometimes get enquiries about dark and bright sounding trumpets. Recently someone has asked whether I could make their trumpet dark.
Following is what I have replied. I expect to write a blog on this, but for now, would like to receive comments.
There is not necessarily one component that will make a trumpet dark. Trumpets, unlike synthesizers etc, require a relationship with the player. It is the sum of and relationship between, all components - player's physique, player's (teacher's) concept, mouthpiece, trumpet, idiom/genre - which all themselves inter-relate to produce the sound. Yes, greatly enlarging the throat of and deepening your mouthpiece could serve to darken your tone; you can check this out with a Flugelhorn mouthpiece in your trumpet. However, I suspect that by "dark" you are also referring to "plaintive", the sound striven for by disciples of Miles Davis/Chet Baker.