Kurt, bypassing the color theory discussion, I will cut to the chase, and say that in certain instances, they do work for me- to a point. I use reflectors almost exclusively for high-powered planetary viewing. In every case, the effect is to increase contrast between features that are otherwise very close in hue and intensity. In a world of perfect seeing and perfect color perception, they would probably not be needed. But many times I have found certain features easier to discern when the proper filter is used. People perceive color & hue saturation differently so I'm sure some people won't need them at all. My left eye sees certain colors much more vibrantly than my right- it doesn't benefit as much from filters as my right eye- but since my right eye is dominant and tends to detect details more easily, I use a filter once in a while with that eye. The irony is that filters don't really show you more- they show you less, overall. You never see a much clearer planetary disk, it's not like they aid focus- overall or of a specific color- especially with an essentially perfectly achromatic reflector. But they do help on certain occassions to tease-out subtle features. I have only found them to be useful on Mars and Jupiter- Mars especially. It may be that I've never tried them with enough aperture on Saturn, for instance, but that planet has never revealed more detail to me with a filter. I have seen some festoons much more easily on Jupiter with filtration, and dark markings on Mars as well. I also use the lighter filters, not the dark ones, and have stacked a light blue and light green with some success. And, there have been instances where there have been no features visible that any filter would help with. Most of the filters sold to amateurs are probably not needed, but I wouldn't want to part with my light and medium greens and blues, and my yellow-green. The lowest transmission value of every color is essentially worthless. As always, your mileage may (and almost certainly will) vary. I'm only stating what I've seen through the eyepiece over the past 40 years. Now, what we haven't discussed is using colored filters to facilitate observation of certain solar features, and I suspect the darker filters may have a new lease on life in that application. A solar image can be projected onto a screen heavily doped with fluors, so that the image is actually shifted to a different wavelength- and colored filters can help with the visibility of features brought into the visual range, that are normally beyond it. This is a simplified explanation...anybody remember the "Magic Box"? Those of you with green lasers can demonstrate this effect. Find a piece of real "day-glow" pink cardboard or plastic, and shine your green laser on it. The resulting dot will be either orange or white. If not, your pink sample hasn't been doped with fluors- it's not true "day-glow". But that's another topic, isn't it? ;o)