In my computing blog I wrote a review recently of Energizer’s PROSW2A “Hard Case” swivel head 2 AA flashlight, which can display red, green and white aspects using high brightness LEDs. A friend recently reminded me that these colours are often used to hand-signal trains on heritage railways during night operations. Specifically these colours are referenced in old NZ Railways rule books, where red means, of course, Stop, and various directions of movement of green and white lights are used to indicate a direction or speed of movement in yard operations such as shunting. Although commercial products of this type are available, they are likely to be significantly more expensive than this $60 Energizer model. However the design of this model, for all practical purposes, effectively limits its usefulness to situations where green and red are the predominant colours used, as these are both controlled by one pushbutton switch. White is on another switch and can be on at the same time as the colours, so a red-white-red or white-red-white pattern, or changing rapidly from white to red display, would be pretty awkward to achieve.