^- If you look at the barricade in the far right of the pic. You'll notice it's kind of blue. I have one at the other base that has a red-ish lighting effect. I'm not all that sure how it works. But I think it's something to do with the base lighting. It also may be possible in other maps besides Isolation. I haven't got the chance to check it out. But if anyone does then kudos for finding it.
There are lighting effects on both foundry and Avalanche too. They are the only maps I have descovered while forging. I am sure they are on all maps. Good job for finding this though
Most likely it has to do with a flaw in the gamma matrices of the fields themselves. On most maps with bases, you'll see a blue and a red light, indicating which side is which, but I don't think that Bungie intended the effects of these lights to go so far. For this one, I'm almost positive that it's a mistake on Bungie's part, as the lights for the bases are beneath the ground, and yet the gamma they're emitting is coming straight up through it. The effects on the other bases must be of similar cause. Good find, in any case.
Yeah. Sometimes if you drive a Warthog into a certain part of shadows, it will turn completely black.