Yes, it is correct that most color press pictures are based on the L2 as the red channel, but the one you have found is not the only set that includes an L4 too. There are several under the raw images section on the rover homepage, but you will have to combine them yourself to form color pictures...

As for why the majority of the sets returned is L2 based, I don't know for sure, but I would guess near IR is more useful for scientific studies, and you get to use the R2 on the right Pan Cam to create stereo images(2 is the only filter that are the same on both cameras). Also you save valuable bandwidth on the downlink by not transferring the L4, I guess...

By the way, I seem to remember that the 570nm is yellow sensitive, not red, in fact the chemistry of the cones are not very sensitive to red at all. I seem to remember the peak of this detection is in the blue part of the spectrum, but since only about 2% of the cones have what you can call the "blue filter", the peek for the eye is more towards the green part(I think there were a little more than 30% cones for green and the rest yellow).. The red frequencies is something the brain must compute by comparing how much less the green cones are stimulated than the yellow(the sensitivity does overlap, so the green has some sensitivity even bellow the peek of the yellow..).. But I guess I got far away from the point of this thread...

Anyway, I don't think all blue gets such results, but dye is often very different under IR, and I think the calibration target uses a blue dye that is IR reflective... Whether the sky is discolored or not I guess depends on how much IR light you get from it... Also the uncalibrated images often look too much blue, like the ones in the public Maestro Spirit sets.. Then one have the atmospheric conditions on mars, as I understand it the sky is supposed to be bluish when there are little dust in the air, but I don't know how often that happen(Heh, If the sky here on earth so really is blue, why would it be different on Mars... ;-p)

The argument about the ones who paid getting their what they paid for is a little flawed if they use IR since it is better for science, as the whole point of such a mission is to get the most scientific useful data down, not to waste BW to make pretty pictures for the press, that coupled with that its probably just the best sets that is used as press images will limit the sets with L4s I guess...

Hmm, At least that is how I see it.. But I might be wrong in my guesses about the reasons for the use of the L2 instead of the L4...

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