The tea is made from Yerba mate, a shrub/tree in the holly family, genus Ilex. If you want to try using it for color, you could try making an oil infusion with the dry tea, perhaps grinding it to a powder first. The main plant pigment will be chlorophyll, which is a finicky colorant in soap and tends to fade pretty quickly. If you search for matcha, moringa, alfalfa, wheatgrass, etc. you will find a number of recent threads on how oil infusions and green plant powders behave in soap.