The length of cocktail dresses can be ranged from mid-thigh to knee length

You can decide the skirt length according to your body shape. A mid-thigh length dress is fabulous for a woman with nice legs, while a knee length dress suits for all-figures. However, the lengths of evening dresses are generally from knee length to floor length. Floor length is absolutely the most popular one when you're attending some formal events like a cathedral wedding. It is not appropriate to wear an above-knee length dress in a formal occasion.
Cocktail dresses are available in a wide range of colors and patterns. Bold colors like pink or tiger brindles are sure to turn heads in a cocktail party. Don't worry about that you might be more attractive than the bride in a wedding or you might not look graceful in a bright shiny colored dress in a white tie occasion. On the contrary, you need to pay attention when choosing color of an evening gown. As usual, monotone or uncomplicated color combinations are appropriate for formal dresses. Stay away from the bright hues like red or pink at funeral.
As for the fabrics, dresses and formal dresses are basically the same. Satin, taffeta and organza go well with any gowns. But materials can differ. Traditionally, evening gown or dress is made of heavier materials like velvet, silk, taffeta while dress is made of a mixture of feather-weight silk or wool, a high-quality blend of synthetics and the above materials, but almost always never pure cotton (then it would be a sundress). Also the cut can be different. One thing that stands out as an evening dress is the wide-shoulder cut while one-shoulder or demurely-cut halter can signify the cocktail dress.So, an evening dress and a cocktail dress are alike in a way that they are dresses made of high-end, sometimes luxury fabrics, but, in many ways, that is where the similarity ends. Each is worn for a different occasion, falls to a different length and is complemented with different accessories. Cocktail dresses are a little more casual than evening dresses.
The two beautiful dresses worn by the two princesses had the same ivory color, the same re-embroidered lace long sleeves and the same classy A-line skirt beautified with hand appliqué flowers. The necklines are the elements that make these two dresses unique and different. While Kate's Middleton's dress had a deep V-neck, Grace Kelly's dress featured a more simplistic and modest high neck.