Cornet1

I know very little about specific American made instruments but since nobody with the exact experience has yet replied I'll try to give you something to be going on with.......

The colour differences are almost certainly due to the actual metals in the various parts of the trumpet.

We tend to think of 'brass' as simply a metal of clear character, being much the same in whatever guise it appears in. In fact, brass is an alloy of copper, tin and Zinc, and one of a large family of such alloys. Most brass 'recipes' are mixed up according to the particular needs for that brass. In most cases this is to give the right working characteristics during manufacture or for a particular quality which the finished item will require when it is in use etc. As well as all of the 'recipes' in the cookbook, there are many designer brasses which are computed for specific qualities.

For brass instruments the tonal characteristics of particular alloys when they vibrate is very important to bear in mind when designing the playing characteristics.

Essentially, alloys with more copper will be softer, darker and redder in colour and have a warmer tonal quality,...thus bell and leadpipe section are frequently of 'rose brass' or 'red brass'. Parts for valves need to be somewhat harder to give good machining qualities when the parts are turned.

In good quality English made instruments, you can often see upwards of 5 different brasses when laqueur or plating are removed.