I have three filters (besides a UV filter that is always on any lens I use) that were originally made for black and white photography to add or change contrast by blocking and letting in select color waves. For example, if I were to take a picture of the sky with black and white film using a red filter, the filter would make the sky look darker because the filter would absorb blue and green waves (filters lighten their own colors and darken their complimentary colors.
Color Scheme Designer 3 shows a color wheel and an option that shows complimentary colors. It's fun to play with and is fun to use when planing color schemes. This
website also gives an example of what a black and white photo looks like with different color filters).
Enough technical stuff. Though I do think knowledge of how color filters works is important, the main point I want to make here is that filters can be used in many ways. I use filters
a lot with color film and digital, not just black and white. There is nothing complicated with using them in color because what you see is what you get (rather than blocking colors, everything looks more red, green, or yellow depending on what filter you use.)
Yellow No. 15; Red No. 25
Green No. 11
Some filters are also much stronger than others, like the red filter show above. It made my backyard look like it was on fire!
And this photo was take with a yellow filter for a fun affect. As you can see it isn't as strong as the red filter:
And for this photo I used a yellow and green filter together:
I'm hoping more to encourage experimentation. Cover your lens with crumpled saran wrap or color gels. Take a portrait of your cat with a purple filter. Use things that are generally used for something else and have fun!
p.s. I'm taking a Sunday break and will be back on Monday.