That picture reminds me of painting our bedroom in our new house. When I first glanced at your picture above I thought, why did you leave a bare spot on the railing closest to the house. Then I realized it was the sun reflecting. Now I can't see it as not painted anymore. Like one of those drawings that looks one way and then clicks and looks different.
We painted our bedroom a pale yellow before we actually moved in. To cover an awful looking green. After the first coat it was clear I needed a second coat as it had a definite green tinge. Which I did. When dry I looked at it and thought. What crap yellow is this? Still green showing through. Came back that evening to paint third coat and now it was light yellow like we expected.
Turns out the sun, reflecting off the green trees and bushes outside the window made the yellow look green. One coat would have been enough.