Under the Geneva and Hague Conventions, of which Israel is a signatory, the acquisition of territory by war is inadmissible. Transferring the population of the occupier to the occupied territory is prohibited. Colonisation died and was put to bed a good thirty to forty years before the Six Day War. And Israel is fully aware...hence no legal annexation.
UN: Gaza could be 'uninhabitable' by 2020 if trends continue (AP)
from the article: EU slams Israel’s decision to build new East Jerusalem housing project