A blue one on the front would certainly be useful for causing great anxiety to dangerous drivers! Until you came across a policeman, of course!
I use a 12V 7 amp-hour Sealed Lead Acid (SLA) battery. (think 'house brick'). Its main job is to power a 20W halogen bulb mounted on the handlebars.
The design was loosely based on this site :
http://www.hembrow.eu/oldpage/light/index.html When I first started using the system, I had some problems startling pedestrians on shared paths, so I now have it mounted loosely so I can dip it!
Those flashers are only rated at 1W, so on its own, you could easily hook it up to a smaller, lighter SLA battery. A fuse is essential, though, as SLA batteries are prone to starting small fires when short circuited!