Red Hex under airplanes

[Gunja]

Hi,

probably this is something mentioned somewhere, but I couldn't find anything. Sometimes the hex underneath an airplane is red. Now I know this means the airplane is not getting full supply. In fact it is getting 1 or 2 points less, then it should (i.e. when I press S, the hex has 7 supply but the airplane gets only 6).
What I can't figure out is why? It seems absolutely random to me. Could someone point me in the right direction, please?

[Markiss]

Just a nudge, it means that the aircraft is not controlled by an HQ at all, I believe. If it is purple, then it is not getting the best possible supply that it could, i.e. it is controlled by the wrong HQ.
If I am not exactly right, I am more than sure someone will correct me.

[ivanov]

I think it means that the aircraft would have a better supply, if it was assigned to a different HQ ( usually the one that is closer to the unit ).

[thekman]

I have had planes in red or purple squares one or two spaces from a HQ and even though the plane should be in 6 or 7 supply, it is in 1 or 2 when in the purple or red square. I haven't gotten an answer back as to what this is and why. And my plane is or was under the HQ's control. I will have one HQ in the area or maybe two german HQ. I would love to know what the purple and red squares represent and how to avoid them. I don't really think it has anything to do with who the plane is assigned to, but not knowing, i guess anything is possible.

[Taxman66]

Red hash means the planes are not linked to a HQ.
Purple means that the game/AI thinks the planes would be in better supply if linked to a different HQ. This is not always correct because sometimes that other HQ is not able to link to them (e.g. Minor's HQ).

Important: Planes will not draw increased supply from a HQ they are not linked to. So, for example, even if the supply display says the hex is getting 6, a plane in the hex might be getting less if it is far away from it's linked HQ. In such a case the Plane will get the better of what is being pushed from its linked HQ or the raw supply value to the hex from the nearest/best supply source.

Always pay attention to HQ & Plane placement and linkages.

[Gunja]

Thank you all for the answers, that makes things much clearer for me - and sorry for my late reply.