Pop-Up Boilies.....What Color?

I have been on a pop-up kick these days and catching fair to good numbers of fish while using it.  This morning I went out and landed several decent size mirrors in the 10-13 lb. range (see photo of carp landed this morning).   I was using a small, pop-up boilie along with a kernel of flavored maize on the hair.  The pop-ups I was using were Mistral 6 mm boilies that my friend Paul brought me back from France.  They come in a container that has a load of them in all different colors (see photo).  So, which color is best to use?  I would have guessed white or yellow. However, truth is that all the colors seem to work with equal effectiveness....the greens, reds, purples, etc.  I would have never guessed it.  I suspect that it is more the action since a pop-up gives the bait a buoyant quality rather than the color that is the turn on here.  And, remember, too, there is a kernel of maize along with the colored pop-up so maybe that is what the carp are keying on.  For whatever the reason, this is hot right now and color doesn't matter.