You can see the reference marker on the panorama. It's on the solar panel to the left of the mast. At the top of the panel is a white disk that looks like if ha

You can see the reference marker on the panorama. It's on the solar panel to the left of the mast. At the top of the panel is a white disk that looks like if has an old style arcade joystick sticking out of it. Zoom in on the disk and you can see the (now red dust marred) colour calibration indicators on the square surrounding the white circle.