When H became a K

A fleeting thought came to me when Bereishis was read in schul on Yom Tov. The words are "be-tzelem elohim" and not "be-tzelem elokim". I mean, of course I knew that already. But it's interesting how conditioned we become to things. The phrase "be-tzelem elokim" is so popular that it and not the real thing sounds authentic to me.