I've used Rooibos tea. Made it triple strength, let it cool, and just used it in place of my water. Did nothing else special. I doubt any of the great antioxidant properties survived saponification, but it is a lovely caramel color.
I am not distilling EOs (yet...) so using teas is a nice way to put some of my garden into some of my soaps.
I use rosemary tea, citrus leaf teas (petitgrain EO is made from distilling citrus leaves), calendula tea, rose hips tea, spearmint tea, coffee (coffee is a tea right?..... I have lots of sage, thyme, melissa, lemon verbena....I use them when they go well with the other ingredients in the soaps.
Genny is right on the colors. Citrus leaf tea turns a weird bright orange yellow as soon as you add the lye. The soap does not discolor that much, maybe a little more tan, that's all.
I have made a green tea soap where I used triple strength green tea in place of the water in my lye mix. When I mixed the soap "batter" it looked a really ugly dark brown color, but it did settle down after it gelled and sat in the mold and turned to green. I also added some dry tea leaves to the soap as an exfoliant.
I have used tea in a recipe I posted in gallery, http://www.soapmakingforum.com/f22/lemon-star-anise-33220/
It takes tea with lemon pepper marinated in extra virgin olive oil. It is an incredible soap and wore lemon juice decoction skin peels, seeds and pulp with star anise. If you need my recipe I can pass but in the Spain we use a calculator very different with very different results to which you expose yourself here