Then, if you want a blue/green split as shown in your screenshot, open the PhotoRendering Settings dialog's Background panel as shown here and set the background to 'Colors' and select your two colors.
Or, select the Picture that you want. Note that neither the color 'horizon', nor your photographic image (Picture) will move in any way as you navigate.
If you want to navigate with a blue sky and the sense of a green ground surface, then make both colors blue, and add a green/grass covered round slab to your model ... a really huge round slab...
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB