With layers in Photoshop one can make changes so that the image does not reflect reality.
Out walking a day or two ago we passed this alleyway. I photographed it for the shapes and then looked at it on my computer just now. The patch of blue was still a patch of blue (cue prisoners looking out from their cell windows), but the wall at the top nearest the camera implied that there was sky directly above.
So I darkened the wall to see what it would look like. I isolated the light area above the arch nearest the camera and copied it and then set the new layer to ‘Multiply’. That preserved the detail in the wall and darkened it. It duplicated that layer, which was automatically set to ‘Multiply’ and so it darkened the area still more. One more duplicated layer and it was dark enough.
Except there was a lot of aqua in the layer because the wall was not white. Ot perhaps it picked up reflected light from the sky. However it was, I went back to the beginning and this time I desaturated the colour in the arch before making the new layers.