You can set up the light color by clicking "chose" on the gray Light Color bar in its properties. Brightness is often picked wrong then, and the saturation may need additional tweaking, but at least the hue is pretty accurate. It gives you a convenient starting point either way although you may have to tweak teh values "by hand" bit anyways.
Brightness determines the brightness of the light. 0 = the light is basically off. The higher the value, the brighter the light. 255 is NOT the maximum, although I recommend treating it as if it was. You can, for example, create a light with a brightness of 400. I don't recommend it though, because it gets buggy sometimes and after a few rebuilds it may look strange. If you really need lights that bright you can use more than one light as they add up of course. Seems to be less buggy. Also, high brightness often means your colors get distorted. E.g. a very, very bright orange light becomes green. Just keep your eyes on that and don't let it happen as it looks ugly.
Hue determines the color of the light.
0 = red; 35 is a good yellow-orange like color for lights; 50 is yellow; 80 = green, I think; 135-140 is slightly greenish blue; 160 = blue; 180 starts to get violet and 255 is red again.
Saturation determines how strong the color is. 0 means the color is pure and the closer you get to 255 the more it gets grayed out / whited out with 255 making every hue white.
When I set up the color of a light I generally just experiment with the values and don't even touch the "chose" thing. Starting from a newly placed default light I first set the brightness roughly to a level I like. Then I tweak the light radius. Then I rebuild changed lighting because the real-time preview isn't 100% accurate. I continue to do this until brightness and radius are correct. Then I set the saturation to 0 so I can get a clear view of the color. I know the hue values very, very roughly so I roughly know where to start and then I go from there. E.g. I know what 35 looks like, roughly, but then I decide I want it to look warmer, so I try 32, 30, 28, etc. Or I want it to look more yellow so I go in the other direction and try 37, 40, 45... If you don't want to do that you can just pick a color you like from the MSPaint-like color spectrum thingy that opens when you click "chose". The UnrealEd seems to get the hue pretty accurate.
Then, finally, I adjust the saturation.
Then another rebuild and if I like what I see that's it.
As for methods of lighting maps, it totally depends on how you like it better. Concerning both the look as well as the process of setting it up. Here are some ways:
The most realistic, although impossible to realize variant is the following:
You simulate the global illumination from the sky around the earth, by having an infinite number of sunlight actors that are all on a globe and point to its center. Then you add one much brighter sunlight that shines in the direction of the sun. Apart from light that bounces off surfaces this would be the perfect simulation of outdoor lighting. Unfortunately it's not possible to do that in UnrealEd. For one you can't have an infinite number of sunlight actors and even if you cut it down to, say, 100, you can't make their brightnesses lower than 1 respectively and combined that's still 100. So you'd have to go even lower, to, say, 10 or 8 and then you'll still run into problems. E.g. weapons tend to flicker when too many sunlight actors hit them and the colors get very buggy. My map KF-Dammage is lit with this method and it was a real pain to set this up, but in my opinion the lighting turned out great. Check out some screenshots here:Click me!
If you go even lower (3 or 4 sunlights) you'll eventually arrive at the solution below:
You can use multiple sunlights. E.g. one slightly orange colored (hue around 35) for the main sunlight and two or three blueish sunlights (hue around 150) that shine in the opposite direction so shadows aren't pitch black. Then you end up with a relatively realistic looking environment except in areas where all sunlights are blocked and you still have pitch black shadows. Those areas you can light with individual, regular lights.
Or you can ditch the opposing sunlights completely and have one sunlight for the sun and light up your shadows (i.e. simulate both bouncing light from the sun and global illumination by the sky) entirely with regular lights.
It's quite a bit of work to get this right, especially for a big map. My map CTF-Wasnuni was lit like that. It's an indoor map so there is no sunlight, but I still eliminated pitch-black shadows with this method. Screenshots are here:Click me!
You can also take a shortcut and use one slightly orange sunlight for the sun and eliminate the pitch black shadows with zone lighting instead of some opposite sunlights! E.g. have a slightly blueish zone light with a brightness of, maybe 8 to 48. Maybe less for night maps. That way everything will be lit a bit but you still have highlights and shadows from the sun. It doesn't look quite as realistic as the methods above, but it looks pretty good and is very convenient to set up. The main problem I see with this method is that there is a bug in the engine that makes StaticMesh react to ZoneLighting twice, for some inexplicable reason. So if you have a brightness of 32 for it, StaticMeshes will be lit with 64, which is pretty much considering 128 is unlit. This makes StaticMeshes stand out a bit from the rest of the environment.
My map KF-NorthSea is lit like that. Check out some screenshots here:Click me!
As an additional tip: When you are completely done with your lighting and you think it looks realistic now it can be cool to place some highlights. By that I don't mean things like street lamps but just unexplained highlights that could simulate the varying reflectiveness of surfaces. If you get it right you can give your map a very slight "next-gen" touch with it. I did this in KF-Dammage, for example. The "feet" of the dam have subtle highlights on them, for example. Feel free to check it out both ingame and in the editor. This can of course be done regardless of the method you chose to use to light your map.
Your choice, really. It depends a bit on the map (e.g. I wouldn't want to light a huge out-door map like some tank maps for Red Orchestra with individual lights and if I care for rebuilding-times I wouldn't want to use the method from KF-Dammage, but in the end it's your decision.
If you can tell me the time of day and the weather conditions of your map I can give you some more tips. Also the above are only artistic guidelines, so to speak, so if you have a technical problem with any of those, feel free to ask. It took me a while to see this post because I was so used to this forum being dead and only the tutorial section seeing some action, but I'll check by more often in the next couple of days!