If the Screen printing is conventional, each colour means a machine step and therefore increases the production time, and price.
Indeed, in the front panel with matte finish, total transparency is achieved with an extra coating step causing a machine step, and increase cost.
In the coloured areas, each colour (for example red, green, yellow, …) means a step machine, and increase cost.
The front panel is a sheet of polyester or polycarbonate with a screen printing. Usually carries an adhesive on the back. For indicating a switch is placed in a box containing a mechanical switch below. But it is only an aesthetic and “closing” piece.
The switch includes in itself the (LED, SMD resistors, etc.) keys and has an output wire with different routes. It stands on a box that only needs a slot for wire passage.
There are several ways to prepare a membrane switch. In fact, the membrane keyboard “pure” are two sheets of polyester with printed conductive ink contacts facing closing contact when pressed at the same time. This is the lowest cost model. Following the economic order, may consequently take advantage the same technology and print a conductive ink on polyester top placing in the contact areas, a metal dome, which will subsequently covered by screen printing. This improves the tactile sensation, with feedback to the press, and the typical metallic “click” sound.
It can also be made by substituting the same switch polyester printed with conductive ink by a printed circuit board. This improves the conductivity (resistance of the tracks is reduced) and allows other paths, placing SMD components from the reverse side, much more room for connectors, etc.
No. Keep in mind that the keyboard wire in a flexible membrane cannot pass through the space occupied by the keys. Also keep in mind the need for all tracks reaching the area of the wire space, which should be free of keys. In general, if you can draw on paper, can be manufactured.