Hi there,
It seems that selecting a color in the customizer may affect both the mobile AND desktop.
That is correct – there aren’t separate options in the customizer for this and it’s rarely requested.
However, a workaround solution would be to use the off-canvas menu for mobile only:
https://docs.generatepress.com/article/off-canvas-panel-overview/
Then you can use the Off-Canvas Panel under Customizer > Colors to modify the colors.
Let me know if this helps 🙂