Don't use retail sites to define dress codes. They are over-inclusive because they want to put as many options in front of the customer as possible. Cocktail attire means a formal dress that is around knee length with or without a slit. You could do ankle length, but not floor length. It can have any sort of sleeves or even be strapless. Cut and fabric should be formal but that is somewhat flexible depending on the venue, season, and time of day. Dark colors typically read more formal, but again what is appropriate in terms of color is situation-dependent. Red is completely fine unless the couple is from a specific culture where red is either taboo or worn by the bride. For most American weddings there is no problem with wearing red. Some examples: https://www.lulus.com/products/hollywood-woman-forest-green-satin-midi-dress/696052.html https://www.lulus.com/products/baby-you-re-the-one-black-sleeveless-bodycon-midi-dress/881742.html https://www.lulus.com/products/remarkable-black-lace-dress/503262.html https://www.anthropologie.com/shop/guapa-one-shoulder-mini-dress?category=cocktail-wedding-guest-dresses&color=027&type=STANDARD&quantity=1 https://www.anthropologie.com/shop/amanda-uprichard-silk-mock-neck-dress?category=cocktail-wedding-guest-dresses&color=030&type=STANDARD&quantity=1 https://www.abercrombie.com/shop/us/p/plunge-neck-midi-dress-48406319?seq=03&categoryId=12265&faceout=model1 https://www.abercrombie.com/shop/us/p/satin-cowl-back-slip-midi-dress-49325319?seq=02&categoryId=12265&faceout=model1 Answer from GermanDeath-Reggae on reddit.com