I graduate from high school tomorrow, and I was wondering if it was acceptable to wear a yarmulke underneath my graduation cap. I lean more towards reform, not that that matters :)
Thanks y’all!
Firstly, welcome to Mi Yodeya!
To answer the question, yes, it is not at all unusual for someone to wear a hat or another type of covering over their yarmulke. It does not conflict with the halacha.
Essentially, the reason for covering one's head is because of the gemara in Shabbat (156b) (Credit to Baal Shemot Tovot for translation) which states:
כסי רישיך כי היכי דתיהוי עלך אימתא דשמיא
"Cover your head so that there will be on you fear of heavens"
This is quoted in the Shulchan Aruch as Halacha (O"C 2:6). Therefore, as long as you have your yarmulke covering on your head which imbues you with the "fear of havens", then you are fulfilling this, and thus, it is not a halachic issue if you have a hat over it.
It's very common to wear a hat over your yarmulke and many Orthodox and Haredi Jews do it all the time. See this article on Chabad website which talks more about its spiritual significance and history.