I've done some LED tail lights.
You may as well use the same colour LED as the lense your putting in front of it.
Any other light,as in a white LED,is filtered out by the lense and is just wasted energy.
Contact
www.activecomponents.com for LEDs
I got 4000 mcd reds for 30 cents each per 100
Heres a driver that could be modified to work in place of the flasher
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