I wouldn't do it with a completed garment like a kilt, but it would work with 100% wool fabric.
Tea will work, but if you really want success in "browning" some fabric, find a black walnut tree in your area. They are currently dropping their nuts, and black walnut hulls are an excellent natural dyestuff. Simply gather up a bagfull, put them in a big pot of water over a heat source (outside is best for this operation!), and throw in the fabric when the water is bubbling and black looking. Let the fabric "simmer" in the dyebath until it looks quite a bit darker than you want. Rinse it well in cold water until the water runs clear, and you're done....
Be advised, this is a powerful dye, and will stain your fingers and other surfaces!
Brian
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