Can i say no black at the wedding?

I would say something like beach attire preferred and that should hopefully signal no Black.

Black is a very common safe color that a lot have in their wardrobe for attending numerous events. Telling guests what colors to wear is overstepping especially if it's just for pictures and aesthetic purposes. It would be one thing if you (the bride) were wearing a black wedding dress, but guests do not need to match the theme or décor as long as what they are wearing is appropriate for the event. They are there to witness and celebrate your union, not props for a photo op.

You could tell people that but I wouldn’t get too upset if someone shows up in black. 🤷🏽‍♀️

I personally wouldn’t tell guests what to wear and I wouldn’t appreciate someone telling me.

Why black though? What if people wear navy blue or dark green? Dark colors add contrast. And I don't think it would take away from your aesthetic. Frankly unless you have a theme, guests should be allowed to dress themselves according to the place.
If you really want everyone to where a neutral color then maybe you can get away with having a bohemian theme, and can say "guests are asked to wear a light neutral" But then you run the risk of someone wearing white or close to white.

Black and navy are my go to colors when going to weddings because they tend to be neutral enough to not stand out and go with any color scheme, so I probably wouldn't appreciate being told not to wear that. You can tell people it's beachy or bohemian but some people still won't know what that means. I don't like when people do a color palette because to me that says "you're a prop in my aesthetic" and not "I want you to be comfortable as we celebrate together"

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I second this.

Is your January beach wedding in a place that is hot? If so, I doubt your guests will wear black sportcoats or sundresses. Also, I would think Bohemian is color, pattern, texture, even fringe. Would that or even Hawaiian shirts be contrary to your aesthetic? If so, I think you should just let go of that unnecessary worry and let adults dress themselves.

If it's actually a cool or cold weather beach, you can provide beige wraps for all of your female guests, neutralizing their clothing choices for your 1-3 pictures.

I got married at the beach and my bridesmaids wore black dresses. It's fine to wear black to a beach wedding and looks beautiful. I don't see anything wrong with black.

No you cannot dictate what people wear. Guests are not props. If you don’t allow black, the men will not have anything to wear since suits and tuxes don’t come in many other color options.