Feeling blue? Or in the pink?

When I worked in Nepal I went through a phase where I thought I was losing it. There were the prettiest flowers on a bush outside the meeting room window of our office, and I could never remember if they were blue or pink.

One day I could stand it no longer and asked a totally bemused colleague, "What colour are those flowers?" He looked at me in a manner which was delivered in an understandably patient and delicate way - the way you would deal with a child learning their colours or a very elderly relative, and he said - "They are blue"

I saw these flowers on the way to work the other morning here in Chennai- the same flowers and they were also blue.

However this time, I knew what was coming. I took this picture to show that they are blue. Then on the way home I took another photo of the same flowers, in the fading daylight. In Nepal I had dragged my colleague back into the meeting room later that same afternoon and demanded - "Now what colour are the flowers?"

I could see his patience wear thin until he looked out of the window and his face crumpled in puzzlement - "They are - PINK?" And they were! So now I knew for sure that these amazing flowers start the day blue and by the end of the afternoon they are pink. I have no idea (yet) whether they suddenly change at some magic hour, or if gradually as the day progresses, they transform into pink flowers!

But they do in Kathmandu and they do in Chennai! Any explanations?