Check the Main Camera Settings > Advanced Settings for "Auto White Balance on Screen" toggle.
Your other tablet probably has it turned on and the green one has it turned off. Both are showing the same data, but the other one changes the color balance before displaying it. Just affects the display, not the RAW data when you save it.
If you want it to look gray, the toggle on, wait for the image in the Preview background to turn color, then return to the Preview window.
Chen