Create the macro as shown by Strife. You'll need one for each of the heals you're using. Then on the Spells tab in Healbot, call the macro instead of the heal directly. So, for example, if left click is Regrowth put myRegrowthMacroName instead.
Back again and have done some more testing. I don't know Lua at all but I used to code for a living so I poked around a bit. I'm pretty sure that creating Lifebloom as a debuff was the source of the problem. I completely removed my custom debuff and the problem is gone, along with my custom bar color alas. (Note from my previous comment that only disabling the Lifebloom custom debuff did not completely solve the problem.) For now I will just live with it this way. Perhaps you could add "custom buffs" or the equivalent as a feature someday, or perhaps the ability to label a custom debuff as a buff. You DO have a monitor for buffs setting but Lifebloom isn't a choice and with multiple tanks it wouldn't do what I want. I doubt there is a huge demand for this kind of feature so no worries. Thanks and hope I didn't waste too much of your time.