Color CCDs have several disadvantages over monochrome ones for science applications: lower sensitivity, bleeding, aliasing, complexity... So normally for color pictures in space, they simply use filters of various frequencies: R, G, B for color pics, but also IR, UV and various peak frequencies of interesting chemicals (very important for science). This way it's not just a camera, but a full on science measurement. Every space camera is used like that. But why wasn't it used here ? Simply because the relative motion was too fast: they already had to use a short exposure time in order not to get a blurry shot, but changing filters take time and the pics wouldn't match in later post-processing. This method only works for subjects that don't move (or if you don't move yourself).