"Blue" vervain, they call it. And they say dogs are color blind.

Vervain is a wonder herb

with a very versatile set of magical uses. It clears stagnant energy and can be used for cleansing and consecrating a sacred/ ritual space and to cleanse the auras of the participants. It can be used to conduct and direct magical energy and intentions and also to open the psychic channels.
Star Child Herbs: VERVAIN - Organic - Verbena officinalis

Vampire Diaries,

the novels and TV show, used vervain as the anti-vampire weapon of choice.

Vervain is a potent herb and a vampire's most well-known weakness. If a vampire makes physical contact with vervain in any form, it will burn them.The Vampire Diaries Wiki

10 Wonderful Benefits of Blue Vervain - Organic Facts

Apr 2, 2018 - The most important health benefits of blue vervain include its ability to stimulate the liver, soothe the nervous system, detoxify the body, reduce depression and stress, eliminate pain, lower inflammation, protect the immune system, and alleviate chest congestion.

There's more, lots more,

if you just surf the net for "blue" vervain or hoary vervain or Verbena hastata.