Wedding dress to brother in laws wedding

Soo I’m having trouble figuring out what to wear to my brother in laws wedding next month and was hoping I could get some advice..I’m not in the wedding so I know I can not wear white-obviously- and not the same color as the bridesmaids-navy. (My go to color of coarse) so I was telling my mother in law that I want to wear maroon because that’s the color of the groomsmen ties (my husband is the best man btw) and I was to trying to match him for photos. She told me I can’t wear maroon because that’s the color she is wearing-fine. I’m not too familiar with all the wedding etiquette for attire so I didn’t know that that was a thing-not matching my mother in law 🤷‍♀️ or husband. So if it is a thing is it acceptable to accent a black dress with maroon shoes or jewelry? Or should I just wear all black-which isn’t my style. I love having that pop of color. Is there any other colors that you can think of that will accent maroon-can I do like a light pink or is that too close to my mother in laws maroon dress? Sorry for the long post I often feel like I walk on egg shells with her so I don’t want to upset her on her sons wedding day- thanks in advance!