Sorry if this bug had already been reported, but a brief search didn't reveal similar threads.
In battlescape, when an alien fires a plasma weapon at one of xenonauts and misses, the ground texture becomes pockmarked. If fighting in desert/arctic environment, this results in green grass texture being displayed instead of charred/pockmarked ground. In arctic - maybe it's moss or grass under the snow, when it melts because of plasma heat But in desert?