Somebody told me in Israel some have the custom of decorating the egg for Pesach (like an Easter egg). Wouldn't that be considered chukas hagoyim or avoda zara?
Well, as Fred's excellent answer over at the other question demonstrates, it is fairly well-established that several different Jewish communities had a custom to dye or colour eggs for various holidays, including Purim, Pesah, and Lag baOmer, in both the Mizrahi world (Yemen, Afghanistan and Kurdistan) and the Ashkenazi world (Hassidic and shtetl customs). I've seen mentions in my reading to decorated eggs used in wedding ceremonies as well in the Afghani community, and this suggests that it was part of Temani weddings as well.
As well, Segal mentions a related custom in the Polish world known as gein af vikup, which refers to visiting one's relatives and neighbours to receive coloured eggs: read (tantalizing hints) more here and here. I've always been curious myself about the relationship between these eggs and the traditional Eastern European tradition of pysanky, which are extraordinarily beautiful decorated eggs, with folk patterns that predate Christianity by many centuries. My friend has taught me the basics of pysanky-making, with which I have made several fairly-successful Pesah-themed eggs for our seder table. I like to think of that as entirely in keeping with the traditions of my Ashkenazi ancestors as well as my broader sense of Jewish heritage.
Without knowing the specifics; such as who has such a practice, for how long, an if there are any sources, then I'm not certain we can presume that such a practice hasn't been consciously adopted the non-Jewish custom. Either way it seems extremely problematic to maintain such a custom:
It is the opinion of the Chochmas Adam 89:1 that when non-Jews establish a practice in the service of their religion then it is forbidden due to Chukkas HaGoy [non-Jewish practices] even if it is mentioned in the Torah that Jews had a similar practice (It would seem obvious that this doesn't apply to that which Jews are obligated to preform, I think our practice to avoid prostrating may be an example of this). If it is done by the non-Jews for no "good" reason then if it is mentioned in the Torah that Jews did so then they may continue so, but otherwise it is forbidden due to Chukkas HaGoy. The example given is there was once a practice to decorate Shuls with trees on Hag HaShavuos but the Gra nullified the practice because of Chukkas HaGoy. I suspect that l'maaseh it might not be as clear cut, but it seems like a very reasonable distinction to apply when faced with an issue. I would be interested if seen how other poskim address this question. https://judaism.stackexchange.com/a/1407/899