My question is regarding attendance of Jewish ceremonies. I hope it doesn’t make my question any less important if I’m not Jewish - it relates to showing respect to Jewish culture. Basically, I feel uncomfortable to use a kippah since I don’t want to pretend what I’m not, but I also don’t want to offend people by not observing the custom. As I understand "any head covering would do", so I was wondering if it would be ok so customize the design I would put on my kippah, but not so to be offensive either. Maybe I can send you a photo of the design to hear if you would approve.

You don't need to wear a Kippa, but as you said you don't want to offend anyone and some people will mistakenly think that you should wear a head covering so it is just an idea of the right tact. You can wear any head covering.