Surely one should look at power rather than current.
Since you mentioned a cluster of them, would that be to achieve brightness?
Luxeon LEDs are worth having a look at.
If you go with white over blue, you'll lose some photons.
Whether you want to go with red, red-orange, blue or green will require you to weigh up the power draw vs luminous flux vs other constraints*
Red has a much lower forward voltage than green, but the eye is more sensitive to green (eye sensitivity is accounted for in lumen ratings).
As for things far away in the sky, I'm not sure if one color is better than another. Bit tricky, this apparent brightness thing.
To get the most out of your batteries(?), you might want to look at a DC to DC converter of some description to keep everything running when the battery voltage drops.
- Legal?