Thanks for this! I've been away for a few days so haven't been able to respond. Basically, I'm only using one mini red led which I've harvested from a fibre optic lamp. It's already fixed to a flashing circuit board and is designed to run off three AA batteries. It's connected to a green and a blue so I'm guessing that a resistor won't be necessary...

I'm also going to be using some white leds in parallel - they have all been harvested from devices in which they are connected individually and without resistors to batteries totalling 6v, so I'm guessing I'll be ok with those too.

I'm going to post some photos of my progress with an explanation of the power source solution you described just to help anyone else who's starting out with this stuff. I'm hoping I'll get more some useful hints and tips from that!

Thanks for the help Grendels!