Jill wrote:

[[While it would be nice if flows were caused somehow by water, I'm not personally convinced that is the case. Certainly the ground could not be dark for years after an event from water alone. ]]

I agree the soil couldn't have remained moistened for very long by these flows, assuming that they're water. They appear to be very short-lived events. That may be why they don't generally form well-developed dendritic patterns.

The original dark color might be the color of the flowing substance or be due to some chemical reaction with soil.

I don't see that the high altitudes at which some of these features occur poses much of a problem for a water explanation. Impurities in water might lower the freezing point substantially. But the images by themselves certainly don't prove that they _are_ water.

[[My current conjecture is that a surface disturbance occurs and it takes years of dust deposition from the atmosphere to "fade" a flow feature.]]

In my opinion, the fact that some of the "seeps" are lighter than the underlying terrain rules out dust as an explanation for the color change.

Also, the lighter-colored seeps are no less distinct from the background than the dark ones. This is in contrast to what appears to happen to dust devil tracks with time. They don't just become lighter in color; they become less distinct and blend into the background. That, I think, is what would happen if dust were the explanation for the color changes of the seeps.

I'm beginning to think that long-term exposure to sunlight is the best explanation for the color change, although this is just a "WAG" (Wild Amateur Guess).