Lungwort

I was doing a bit of tidying up in the garden today, and found the first of the lungworts (Pulmonaria) are beginning to flower. I knew their name derives from the appearance of their leaves which bear silvery spots resembling lungs. However, I've just discovered that the reason their flowers change in colour  from pink to purple as they age (anthesis) is due to a change in the pH value inside the petals,  going from  acidic to alkaline. Why do they do this? Is it a signal to pollinating insects of the  development stage of the pollen and nectar? I think I need to do more research on the how and why.