Coerulea catts

The coerulea (blue) forms of Cattleya are rare in nature and this has given them some desirability among collectors - they are often more expensive than other color forms (and often less vigorous).  I'm not into them myself, but I stumbled across this set of articles summarizing one man's decades long scholarship and investigation on this topic.  Impressive. 

One interesting point is that in Cattleya breeding crosses between highly diverged species often produce hybrids having the same coloration as the parents.  This suggests that the genetics are simple and that the same genes are often responsible for a given color form in many species.  This is an interesting evolutionary phenomenon.