Eflares - which colour?

Hello all,

I have just been looking through the Exploroz online shop to get kitted up for our next trip. I noticed the Eflare safety devices - they seem like a pretty good idea and are available in 2 colours, red and amber. The description of the items doesn't differentiate between the use of either colour. Is there any protocol or standard for the use of either colour, or is it purely a personal preference?

Thanks in advance.
Jezza.