Butterfly bushes (Buddleia species) do not naturally bloom in three different colors, so I assume the ones you obtained were grafted. Very often, one or more of these grafts will fail and you will be left with a single color, sometimes that of the understock, which is probably not what you wanted at all.

FWIW, generally these types of plants are most often found through less reputable sellers......like Michigan Bulb, who is notorious for multicolored, short-lived Frankenplants and zero customer service.

Here's another thread over in the Butterfly Forum...

Here is a link that might be useful: Butterfly Forum thread

Hahaha on me; that's your thread, LOL, sorry!!!

I am having the same issue with mine, after talking to the local nursery
they said feeding it holly tone, and aluminum sulfate will fix the
issue. If the plant has already bloomed this year then you should wait
to feed when you prune it down. Hope this helps and works, guess I will
find out next year.