Color filters can be very useful for enhancing your views of the Moon and the planets. Depending on the atmospheric conditions, the telescope being used, the observer's experience, and the planet being observed or photographed, the advantages of color filters can be anywhere from subtle to dramatic. The right filter can make all the difference between seeing several small craters in the floor of Clavius on the Moon or not; seeing five or six swirls in Jupiter's belts or not; or seeing the inner Crepe Ring of Saturn or not.
GSO's 1.25" color/planetary filters are manufactured from the purest optical glass and are dyed-in-the-mass (not simply "color coated") for premium performance. They thread into the barrels of virtually any 1.25" telescope eyepiece. Each filter cell has a male and female 1.25" filter thread (M28.5x0.6) on opposite sides, so multiple filters can be stacked to achieve selective filtration of the visual color spectrum. The clear aperture is 25.6mm and each filter comes in a protective plastic storage case. Made in Taiwan.
The #29 Dark/Deep Red Filter functions much like the #25 Red, helping with daylight observation of Mercury and Venus (particularly the Venusian Terminator), the Martian Maria and polar caps, Jovian Belts and for Saturn's clouds. It has also been reported to be handy for observing the transits of Jupiter's moons across its disk. However, because of the reduced light transmission, the #29 can only be used on larger telescopes with over 8"-10" of aperture.
Agena Informational Article: Choosing a Color / Planetary Filter