The green section of the graph represents ice or the solid phase. This is an area where there is a high pressure but lower temperature. The yellow section represents water or the liquid phase where there is neutrality in pressure and temperature. It is also referred to as the stable phase. On the other hand, the blue section represents the gas phase. The gas phase is generally an area where both pressure and temperature are high.
The yellow line indicates sublimation. Sublimation is the transition of a substance directly from the solid to the gas phase, without passing through the intermediate liquid phase.
Following the things I've mentioned, at 12.00 atm and -40°C, the matter is supposed to be at its liquid phase.