Great question, Olivier.
The main body of the melodica is typically a tray in which the keyboard and the inner works sit. That tray is plastic on the Yamahas and metal on the better quality Suzukis, wich I call the metal tray Suzukis, such as the M-37C and M-32C. The keys are white and black as on a piano, except for some Hohner Melodicas with multi-colored keys. Then there are the end pieces that may slide in and cover the whole end, as on the Suzuki, or may sit on top at the ends of the keyboard. There are some other configurations on some models. Then there is the button or lever (button on top on the Yamaha, lever that’s depressed at the end on the Suzuki) for the spit valve.
On the Yamahas, the tray, the end pieces, and the spit valve button are the same color. But if you refinish one, as I have done with my P-32D, you can get a nice visual effect by painting the end pieces and tray, and even the button, in different colors. On the Suzuki M-32C, the tray is blue, and the end pieces are a nice white (a cream color, actually). So it is more accurate to say it is two-tone in color, rather than referring to it as blue. Almost all mouth pieces are black, and the black mouthpiece adds to the over-all look of the Suzuki M-32C and some other Suzukis. The plastic spit valve lever is the same cream color as the end piece. The strap on the bottom is also black. In my opinion all of this creates a look of quality on the M-32C, and I think it is a very handsome melodica.
The strap is black on almost all melodicas.
We have had some discussion of how the color of the melodica affects our aesthetic experience and perhaps even our playing as we are using it. Although you are not seeing the melodica as you play it, Olivier, it probably is meaningful for you to have a sense of what it looks like. But the feel is also important. Both the Yamaha and the Suzuki models we’re talking about are very solidly built and feel good to hold. I like the way these 32 key models balance in my left hand, especially the Yamaha, though the Suzuki has an especially solid feel to it. I don’t use the strap.