Alan B said:
What's the best color for downlighting? Red in the rear and white up front?
Best might be relative to yoru situation, but I use white because it lights up everythign better. Since older license-plate-lights would light up the ground behind and around the back of a vehicle with white light anyway, it's where I got my inspiration to use them all over.

There is a product called the Down Low Glow that uses (or used) CCFL tubes inside clear protective tubing. I was going to do that, at one point, but never did, as theyr'e so fragile I broke some just trying to get them setup. :/ But when LED aquarium strips came along supercheap on clearance, I jumped at the chance and strapped them on the bike. There are even cheaper and better ways of doing it, less fragile, but that's what I have.
As long as the actual light source itself is not visible to the rear, then in most places there's nothing illegal about having white light shining on the ground around the vehicle, or even lighting up the vehicle itself.
For instance, in an old scifi show Babylon 5 there are large towers on some of the ships specifically to hold lights to shine on the ships themselves to light up emblems, names, etc. While I wouldn't really wanna put stuff sticking out teh side of a car or bike to do that, if I already had a place to put them I'd be willing to.
ON my old DayGlo Avenger, I had planned to use UV LEDs under the bars and seat to shine on the dayglo paintjob, causing the bike to appear to glow at night. I never got past a quick test of the theory using some low-brightness LEDs out of an old cmputer fan, but the idea worked.
I've thought a number of times of placing white LEDs of very high brightness in similar places, to ligth up a regular bike itself, and the rider, without shining the lights on anything else. It'd require masking off parts of the light cone from each LED, and would be a PITA and very time consuming, but it would make an interesting spectacle and certainly make it easier to see the bike/rider at night.
But downlighting in white is about as far as I've gotten on a permanent basis.