I'll take a stab. Let's look at one line, the cyan one, reprsenting the data from some part or all of the cyan circle.
The line is made up. It's not really there, but just educated guesses as to what is between 11 firm data points. Those data points reflect (heh) measurements taken from 11 photos of the area taken with 11 different filters in front of the cameras -- i.e. measurements of brightness of the area when viewed through filters that allows different very narrow ranges of light frequencies through. See [link]
for a nice chart of the filters.
The vertical bars probably represent the range of brightnesses measured when examing the individual pixels within the area of interest. The squares upon the bars represents some kind of average brightness for all the pixels examined.
So what does it tell you? It tells you how the cyan area reflects light of 11 different narrow ranges of light frequency. That tells me almost nothing -- because I don't have tables of how certain materials reflect light. But, to someone who does, it tells what possible material or materials behave similarly to the one or ones in the area of interest. Possibly it leads to exactly an indentity of the mineral in question. More likely, it eliminates a lot of possible materials and leaves one with a relatively small number of materials to consider.
That cyan line genrally says the cyan object is very gray. It is a fairly flat line, and therefore is reflecting almost equally all the different frequencies. It's not predominantly red, green, blue, or even various infra-red and ultra-violet colors.
The different curves vary enough to show that the different areas are made of different materials. Which ones, I know not.
Base strata? Yeah they could do that. They might have. They just presented a few areas here, as an example of what can be done. Every picture tells a thousand stories. That's a lot of data. Amateurs armed with the known reflectance of materials could probably parse apart brightness levels of objects in raw images, or much better the uncompressed high resolution images that NASA lets trickle out, if they wanted. I personally have no desire.