Anime - Shown in the UK in 2000. Had a woman with long white hair, a green outfit, and a red jewel in her wrist

Question

It was an anime that was on TV (probably Cartoon Network) in 2000 in the UK. It was a fantasy series. One of the moments that stands out was a white haired woman with long hair, a dark green outfit, and most importantly, a red jewel on her wrist.

Answer 1

Tenchi Muyo!

You're probably thinking of one (or more) of the series in the Tenchi Muyo! franchise, of which the first three aired in the UK on Cartoon Network's Toonami programming block in the early 2000s.

The English dubbed versions of the first 13 episodes of Tenchi Muyo!, then Tenchi Universe and finally Tenchi in Tokyo (simply listed on IMDB as different seasons of a single series) all aired sequentially several times on Toonami in the early 2000s (first airing in the US from June 3 - September 29, 2000). This may have been confusing (it was certainly confusing to me) as each series is essentially a reboot of the premise and significantly changes the story compared to the previous instalment, but they were broadcast sequentially without explanation. In general, each series is basically a sci-fi/fantasy harem anime about the protagonist Masaki Tenchi having his peaceful life troubled by an expanding collection of alien/magical/spacefaring women.

Each series shares the same core cast of characters, including the character of Hakubi Ryoko, who is probably the one you are referencing in the question. In all series she is a "space pirate" who finds herself on Earth tangled up with seemingly normal young man Masaki Tenchi - the precise details of her backstory and her power level vary significantly between the different series. She is however reliably depicted as an attractive woman with long white (or at least grey or light blue) hair. She didn't have one consistent outfit but did sometimes wear something mostly green:

In the first series, she has a relationship to a set of 3 magical red gems which can be embedded in her body to power her up; one can be embedded in each wrist, and the third went in her throat (in later series the gems were seemingly incidental or absent):