Here's why:
* Pallor refers to an unhealthy paleness of the skin.
* Color is the opposite of paleness, implying a healthy and vibrant complexion.
* Ruddy specifically describes a healthy, reddish complexion, often associated with good health.
* Flush implies a temporary reddening of the skin, often caused by excitement or exertion.
The best antonym for pallor will depend on the context of your sentence.