The Lumicon Blue #80A 2" filter is blue. It is used to balance daylight film under artificial, tungsten or standard (household) incandescent lighting. Helps place colors in their proper prospective so that when you are looking at a planet under "warm" light, the planetary colors appear as they should.
This filter allows you to "balance", i.e. bring back, correct color tone to your images. There is some loss of film speed that may require the use of a tripod but, at least, your photos will demonstrate the proper tonality they so richly deserve.
For planetary observing, color filters bring out the most detail because planets are naturally colorful. Different colors bring out different details of the planet you are viewing.
Always remember that you want to use the darkest filter your telescope will handle. Most small telescopes up to about 5" in aperture use the light colors. The larger the telescope, the darker your filter you can use. Color filters can sometimes be used in conjunction with a Neutral Density or Polarizing filter to aid in glare reduction. The more you use your filters the more you appreciate them and their affect.
The 1.25" filters employ industry-standard 1.125" x 42 tpi threads (except for Questar/Brandon, which use a thread pattern unique to Questar). The 48 mm filters employ industry-standard 48 x 0.75 mm threading, which thread into 2" eyepieces. All larger filters use the given size with 0.75 mm pitch (e.g. a 72 mm Minus Violet filter has 72 x 0.75 mm threads).