The blue color used to be a common complaint. Now lights are available in neutral white or even warm white. I recommend neutral white (5000K). If a light is offered only in cool white or the color is not specified, look elsewhere. Some people foolishly choose cool white because it gives them a few more lumens. The plain fact is that these days LED's are so bright that you will rarely if ever use the maximum setting, even with a neutral white light.
Here is a random tip: If you find yourself needing to hike a trail at night, figure out a way to fasten your light at waist level so the light is near where your belt buckle would be. This lighting angle gives a lot more information about ground features than light coming from near your eyes.
I have been quite happy with gear by Princeton Tec. They got their start making lights for scuba divers, but now have branched out into larger markets. The following is my description of their lights that I either have or am charmed by. I think I would buy the "fuel" given that I like the concept of a headlamp for backpacking use.
Princeton Tec Aurora
(old model, no longer made, see the "fuel")
2.8 ounces (with batteries), 3 LED's, uses 3 AAA cells. Costs about $22. A headlamp with 3 brightness ranges. On high expect 50 hours, on medium 110 hours, on low 160 hours. I have a couple of these that have had a lot of use and are still going strong. You need to be careful replacing batteries, as it would be easy to break the plastic latch on the battery compartment.
Princeton Tec EOS
(this might be the headlamp of choice!)
3.7 ounces (with batteries), Single 1 watt luxeon LED, uses 3 AAA cells. Costs about $39. 50 lumens with regulated output. 3 brightness levels. Lots of double talk about battery life, looks like you get 1-2 hours on high, and up to 28-50 hours on low. The manufacturer claim of 120+ hours just does not make sense. Well engineered battery compartment. The newer "rebel" version is recommended. If you actually have to hike at night, this will do the job. It can use lithium batteries if you expect really cold temperatures.
Princeton Tec Fuel
2.75 ounces (with batteries), 3 LED's, uses 3 AAA cells. Costs about $25. This looks like it might be the modern version of the Aurora healamp. They claim it gets 35 lumens (presumably on the high setting) for 74 hours. It has 3 ranges: high as described already, medium with 120 hour burn, and low with 164 hour burn. Looks like a nice unit.
Black Diamond has an almost impossible to find website, which I found surprising and annoying. They do make several good looking headlamps. Their lightest (the 1 ounce "ion") strikes out by requiring a unique tiny 6 volt battery (I guess that is the price you pay for such a tiny lamp). They have a multitude of other models, including four that use AAA batteries and each weigh 2.8 to 3.0 ounces. These are the "spot", "gizmo", "cosmo", and "moxie" Prices range from $20 for the gizmo (with 2 AAA cells) to $40 for the spot (with 3 AAA cells). The spot is well liked by people who use it. Weights are the same among their AAA lights, so you might choose the spot (with a 1 watt led and 100 hours on the bright setting) if you don't mind the price. Too many choices? Take a look at build quality and try to figure out light output. They don't provide lumen ratings, but instead give a table of "distances with fresh batteries" and a long explanation about why they do things this way. Maybe they are right, but nobody else is using their system, which means you can only compare their lights among themselves.
Fenix is a niche manufacturer of very high end LED flashlights, as well as headlamps. Their HP10 headlamp uses a single Cree XR-E (Q5) emitter and can crank out 225 lumens. It uses four AA batteries, and has 4 brightness levels (7, 50, 120, and 225 lumens). The 7 lumen mode will go for 210 hours (over a week!), the 50 for 22 hours, the 120 for 7.5, the 225 for 2.5
Petzl has a snazzy website, a broad product line, and lots of information. My experience with all of their products is that they are absolutely top notch, cutting edge, the best (so much for jokes about French engineering). They have a "headlamp performance" table that does include lumen output, so they get my nod over black diamond (who is gaining a reputation for not publishing hard facts and specifications, never mind having a "stealth" website). I'm just too lazy right now to try to sort out the massive Petzl lineup. I do own one of their lamps, the Myo XP (which uses 3AA batteries and yields 85 lumens at the max level). 175 grams. It is a superb headlamp that I have mounted on a caving helmet. Definitely not ultralight though. One of their Tikka or Zipka would be what you want.
Just reading on a caving forum (a great place for information on headlamps) and I discover that there is a very strong following among cavers for the Petzl Duo. This light has a cluster of 14 leds side by side with a single emitter. Here is a thread describing a do it yourself project to replace the single emitter with a Cree XR-E (Q5 bin) emitter.
I just saw one of these in a store. It is a tiny thing and uses a pair of CR2032 lithium coin batteries, which have up to a 10 year "shelf life" (shelf life, i.e. low self discharge, along with suberb performance at low temperatures is what lithium batteries are all about). This little gem weighs 27 grams, and has a little pod-like red carrying case. It is marketed as an emergency light, can provide up to 45 hours of light. 1 ounce is 28.35 grams, so this little thing weighs 1 ounce (with batteries and case). Maybe too small, ultralight fanatics do use it.
Petzl has a warning out about rechargeable batteries in some of their Myo headlamps (models which have a separate battery compartment and a cable connecting to the lamp). In the very unlikely situation where a short-circuit develops in the cable, rechargeable batteries (unlike wimpy alkalines) can deliver enough current to cause a fire or burn hazard! This could certainly be an issue with other brands as well, perhaps only Petzl is being forthright about it. Make your own choice. Any such thing will be happening inches from your face and eyes.
I avoid lights that use "specialty" batteries like the ubiquitous CR123A lithium.
Lithium batteries could be just the thing though
if you do a lot of stuff at sub-freezing temperatures.
However I have been reading that the Sanyo Eneloop rechargeable NiMH
actually offer better cold weather performance than lithiums,
so that argument fizzles.
Plain vanilla AA or AAA batteries for me.
If you do need exotic batteries, here are some sources:
Tom's hiking pages / firstname.lastname@example.org