Yellow flowers in bloom

I have this... theory, I guess I'd call it. It seems to me that the flowers that bloom are grouped by colour. So, one moment most of the blooms will be yellow, the next moment, blue, the next, white. I haven't any idea how accurate this is - it just seems that at the moment, yellow is a predominant colour.

The flowers in the foreground come from my mother-in-law. She calls them Japanese Buttercups, but Google doesn't know about them. I think I trust my mother-in-law more than Google, so Japanese Buttercups is what I'll refer to them as. They are very vigourous - they seem to expand every year. This lot started out as one plant!

In the background are yellow coreopsis. Google tells me that the name comes from the Greek word meaning bedbug, of all things. Apparently, the Greeks thought the seeds looked like bedbugs. Who knew? These flowers seemed to spread for a few years, then they died back. I'm not experienced enough to know if this is a natural cycle or something I did to them. They seem very hardy, and if I remember to pluck the old flower heads, will continue to bloom for quite a while.