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http://www.jebiga.com/seil-bag-led-backpack-for-cyclists/
Looks pretty fancy, but not sure if its practical. Also no 'swearwords' option (yet).
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The problem I see with any new product of this type, is that drivers may well not realise what it is. A certain 'vernacular' has been created with flashing LEDs for bikes, and drivers recognise them quite readily. I don't think introducing different colours (not sure about the legality of that product in the UK) will help things much, as it's simply more distraction for drivers, especially if set against lots of other lights in urban areas, as that picture demonstrates. What you want is something that stands out against all the other visual confusion, which bright flashing white and red LEDs do. No need to confuse things further.