People who are unfamiliar with kimono often assume that the brightest and most elaborate one must also be the most formal. A dark, simple-looking kimono may seem closer to everyday wear. Kimono do not always follow that visual logic.
Their level of formality depends on several elements working together: the material, background color, placement of the patterns, the presence and number of family crests, and the obi and accessories worn with them. Among these, family crests are an especially important sign that a kimono is intended for a formal occasion.
Even Japanese people who know little about the detailed rules will usually recognize that a black kimono with crests is not casual clothing. Depending on its design, it may be worn for a wedding, funeral, or another formal event. A colorful kimono covered in beautiful patterns may look more impressive, but that does not automatically make it more formal. In kimono, visual impact and level of formality do not always move in the same direction.
The kimono alone does not determine the final result. The obi, decorative cords and cloths, footwear, and other accessories must also suit the occasion. A formal kimono paired with an obi meant for casual wear can look mismatched to someone who knows what to look for. It is rather like wearing formal Western clothing with everyday shoes: each item may be perfectly good on its own, but the combination feels wrong.
These distinctions matter most at events such as weddings. A wedding is a formal ceremony, so attending in a kimono considered everyday wear or fashionable casual wear may be seen as more than a personal style choice. A Japanese guest who does this could be judged as lacking basic manners or common sense. The formality of a kimono is not a ranking of price, beauty, or craftsmanship. It shows whether the clothing is appropriate for the setting.
A foreign guest who makes a mistake will usually be given more leeway. People are likely to assume that the rules were unfamiliar rather than that the guest intended to be disrespectful. Even so, choosing a wedding kimono based only on appearance is risky. The safest approach is to tell a rental shop exactly where the kimono will be worn and let the staff select the obi and accessories as well.
Kimono can certainly be enjoyed freely in many situations. At a formal event, however, one beautiful kimono is not necessarily interchangeable with another.