<p>Find the color dye you want and reduce it. Be sure to reduce with the same substance as the dye's base (i.e., spirit-based die use a spirit reducer, water-based dye use water).</p>
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<p>I have found it difficult to get a nice even dye with a really reduced dye. Definitely practice on some scraps before working on your bag.</p>
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<p>Another option may be to apply a finish and dye over top (like an antique finish) -- dunno about that though.</p>