I'd like to see a photograph of them - there is, as far as I'm aware, no white variety of this plant.

Where they in flower when you bought them and was the flower blue then?

In my experience, the blue disappears when the weather is hot.

Not sure its ever hot enough here for that to happen - we've had roasting sun and temperatures of 31 deg C in London, but all the ones I grow are still blue...

I thought there was a possibility, mine did it at 35 deg. C. When it got to 38 deg., they died.

I'm not surprised - not sure I could cope with 38 any more either, lol!