I would hazzard a guess that even if they released L456 combined images, someone would complain that the filters do not approximate the human eye enough. Face it, taking a picture with a CCD/filters will NOT be the same as what a person sees (completely ignoring the fact what each person perceives is different). There are just too many variables, and that is NOT the goal of the mission.
I hate it when people who should know better say this -- I've heard it about Hubble, Galileo, my own CCD pictures and comparing the view through a telescope with published CCD or plate images of the same object. From what you've posted here Phobos, you should know better. What they've released is closer than we've ever gotten before and I would say is a quite good representation of what your eye would see (excepting that these images are at undoubtedly at much higher contrast, since it is a CCD after all).
Looking at the Pancam technical briefing, the only filter shared between the two CCDs is the 750nm (20nm bandpass) filter. Stereo images take precedence right now, since they are trying to map out the surroundings to get distance and size measurements to see where to go next. And I am certain that there is no spare bandwidth right now to send anything more than they are. Bandwidth is the limiting factor right now, and it is a very hard limit, believe me. An extra 25% doesn't exist; heck, an extra 5% probably doesn't exist.
But I would bet that images in other filters will be released in the coming weeks when they have more bandwidth to play with, and the full mission gets underway. But the goal of the first few weeks of any mission is NOT public relations but rover safety and initial science assessment. That is exactly what they are doing. And I would not expect any differently.