EDIT: Apparently nobody read what I said. I did not say can I tell adults what to wear. I said can I even say the decor and such will have fall colors so guests can know ahead of time. I know most people won't care, but I wondering if few would want to know. I never wanted to make anyone feel like they have to wear any color.
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Can I asks guests to prefer fall colors if they can (the wedding is in the fall), but not require it or make it mandatory or make anyone feel like they NEED to buy something totally new just for the wedding?
I'm not looking to control my guests, just give a suggestion to anyone who has many choices of clothes to wear, but not sure what to pick. Or if there's anyone who wants to buy something anyway, or to some guests who I know don't have any formal clothes anyway. If someone wants to wear spring yellow or baby blue to the wedding, I'm fine with it. Is it not polite to make a friendly suggestion? Or is it rude to even say the wedding will have fall decor?