My colors are black white and silver. Formal wedding. Dresses are different styles. Some extended and some tea length. Wedding in July.

Formal wedding: I would have them wear stockings.

Black satin dress: I would say either skin tone or sheer black stockings, preferably black.

What colour are their shoes?
This could aid choose the colour of stockings… if shoes are in white or silver, then sheer skin tone. If black, then sheer black.

Stockings are not hot to wear in summer time. I wore stockings and a lengthy dress to my sister’s wedding in Feburary in Perth Western Australia.
The temperature reached 40 degrees C that day! (104 F). My sister was expecting 45C (113 F).
My sister also wore stockings under her heavy satin gown. She told me a slight swaying of the skirt was enough to help keep cool till the cooling “Freemantle Doctor” sea breeze came in as we left the church for the reception.

For a July wedding, I’d say skip stockings altogether so your bridesmaids may be cool and comfy. However, if it’s a formal evening ceremony, just have them wear normal skin-tone pantyhose. Also, if you happen to be having them wear pantyhose, please have them wear closed-toe shoes. There’s nothing more tacky than pantyhose with sandals.

No stockings, specifically for wedding in July.

Rethink the dresses of varying lengths. How are you going to line the bridemaids up that it won’t look weird having varying hemlines