# An etrog that is completely green is invalid. If, however, if it started to become yellow, it is valid. <ref> The Mishna (34b) cites Rabbi Yehuda’s view that an etrog that is as green as grass is invalid. The Rosh (3:21) cites Tosfot’s assertion that an etrog that is green but will turn yellow over time is valid, since it must be a complete fruit in order for it to turn yellow. Shulchan Aruch (648:21) codifies this view. Mishna Brurah (648:65) writes that the Achronim decided that one should not rely on the fact that the etrog might potentially turn yellow later on unless it has begun to start doing so. Chazon Ovadia (p. 256) agrees. Rabbi Hershel Schachter (“The Halachos of the Daled Minim,” min. 33-5) cited the Mishkenot Yaakov’s opinion that the etrog is invalid even if it started to yellow.</ref>
# See note for a list of other ideal qualities. Besides for the qualities that Chazal specified, the niceness of an etrog includes its subjective beauty. <ref> Bumpy: Rama (Responsa 126) writes that the differences between a grafted etrog and a real etrog include: 1)A real one is bumpy, while a grafted one is smooth. 2)A real one has an indented oketz, while a grafted one has an oketz that protrudes. 3)A real one has a thick peel with very little juice, while a grafted one has a thin peel and a lot of juice. The Tiferet Yisrael (Mishnayot Sukka 3:6) says that a person ideally should look for an etrog that is very bumpy and has an indented oketz. Nitei Gavriel (p. 140) as well as [[Kashrut]] Arbaat Haminim (p. 8) codify this view.
* Ball-like: The Gemara (36a) says that an etrog that is round like a ball is invalid. This is quoted by Tur and Shulchan Aruch (648:18). Mishna Brurah (648:59) explains that a round etrog is invalid since it is not a normal shape of an etrog. Beiur Halacha (648:18) elaborates that it is not necessary to be stringent for the opinion of Tosfot that a cylindrical etrog is invalid, since most authorities disagree. Kaf Hachaim (648:113), however, says that ideally, one should accommodate this view of Tosfot.
* Tower-like: Tiferet Yisrael (Yachin [[Sukkah]] 3:6) writes that ideally, the etrog should be like a tower, meaning thick at the bottom and thin on top. Nitei Gavriel (p. 140) and Arbaat Haminim Lamedharim (p. 252) agree.
* Symmetrical: Tiferet Yisrael (Yachin Sukkah 3:6) writes that ideally, the pitom should be lined up with the oketz. [[Kashrut]] Arbaat Haminim (p. 8) agrees. Arbaat Haminim Lamehadrin (p. 177) cites Rav Nissim Karelitz, who says that this criterion is met if the pitom and oketz are approximately lined up.
* Aesthetic beauty: Chazon Ovadia (p. 278) quotes the Maamar Mordechai, who asserts that besides for the properties that Chazal specified, the beauty of an etrog depends on the subjective view of the individual. Accordingly, Rabbi Mordechai Willig (quoted by Rabbi Eliakim Koenigsberg [http://www.yutorah.org/lectures/lecture.cfm/782108/Rabbi_Eliakim_Koenigsberg/A_Practical_Guide_to_Purchasing_Daled_Minim “A Practical Guide to Purchasing Daled Minim”] min. 44-6) would ask his wife to pick the nicest-looking etrog from amongst the valid etrogim.</ref>
===Placing the Etrog in Wool===