I'm not a big fan of flags, to the extent particularly that they divide and they foment hatred. (Eddie Izzard has a brilliant skit about flags as the tool of colonialists):
BUT if a flag can make a point and unify disparate groups to a common goal, may I suggest a new flag for the NEW SECULAR NATION that must replace an ethno-religious-centric apartheid “Israel” and the divided, decimated remnants of “Palestine.” Maybe we can call it "SALEM" which reflects PEACE as derived from the Hebrew and Arabic words for peace.
To recognize the importance to each of the Abrahamic religions of the land -- Judaism, Christianity, and Islam -- let the flags three colors represent each of those traditions equally, blue for Judaism, white for Christianity, and green for Islam. (I believe these to be the traditional colors for each. Should such a flag already exist, we can change the order, which now reflects their chronological order, or red might also be substituted for white for Christianity)