Certified GKH Gardening Expert
This is Darwin's Natural Selection at its finest! This is a very good example of how a species with a dominant trait can outcrowd, outcompete, and take over a given area. When they are the only left to reproduce, then they will be the only left to show.
You can help prevent this process but it will require digging up and dividing known colored offsets, and only planting the number of each that you desire. Unfortunately, this will be the only way to beat nature at its own game.
The answer missed the point - I am in the north where glad bulbs are dug up EVERY fall and replanted in the spring - there is no bulb separation to do! All bulbs are planted individually at least 6 inches apart - so now what would the answer be? I don't believe Darwinian selection has anything to do with my problem.