Hi Susanne,
That is a cool orchid happening...very cool!
What I know about this particula rspecies is that there is a whole lot of variability in bloom color, and they also bloom when they are very young. I'm not sure if this is one of those species that bloom color will be affected by light and temperatures, but it may be. Usually when this happens however, the results aren't that dramatic.
My best guess is that you've actually got a small colony of plants on your mount, and you're lucky enough to get three different colored siblings.
How neat is that!
Whatever it is, thanks for sharing it with us.