The search engine does what you might call "AND searches" where it tries to find entries that match every parameter you check. If you enter "Tall Bearded", "Red", "Copper/Brown", and "Rose" it will look for tall bearded irises that have ALL THREE boxes checked for Red, Copper/Brown, and Rose. In other words, it thinks you are looking for a flower has that has red, brown, AND rose markings. It does not understand you are looking for any iris with red, brown, OR rose colored flowers.
A couple of other notes about the Iris Database. Most of the information in there was imported directly from the AIS Check List, but descriptions of flower color were among the few things we couldn't get (formatting of the Check List changed enough over time that it was impossible for Dave's program to reliably sort it out) so it all had to be added manually. I'd guess we are about 25% done at the moment. Lastly, relatively few bearded irises are really even close to red, even when they are described as such. You'll have more luck finding "red" irises by checking the box for "Wine" instead of the box for "Red".