Is it permissible for a Muslim woman to wear the hijab, niqab, and gloves with the intention of increasing her fairness, or protecting her skin from freckles and sun sensitivity?

The fundamental principle is that a woman's intention in wearing the hijab is obedience to Allah and seeking His pleasure. The benefit of concealment is achieved through the hijab, even if its purpose is a worldly benefit, such as protecting the skin from the sun. This is not considered a sin, but it may diminish the reward depending on the intention. Mixing the intention of worship with worldly aims does not nullify it, but it may only lessen its reward.