I've got 5 rosa chinensis outside my window and they get about 10 hours of direct sun in conditions of about 39°C and 13% humidity. I water them 1.5 litres per day, and feed them with a bloom special (it has a nutrition chart if needed) every 10 days.
The problem is that newborn flowers (I don't know the technical term :D) are colorful and in colors of orange and red.
but they become white and a bit green after a while.