Be careful with the Tamiya Panel Line accent and test it on a spoon or something that you've painted the same color as your model. I have found that it even starts to attack Tamiya acrylics if its not handled just right. I'd look around and see if you can get Flory Wash instead. Very easy to use, and totally safe on any paint because its water based. Just tried Flory for the first time on my Tamiya F-16 after a near disaster using the Tamiya wash (took my Acrylic clear coat off, and went right after the MM enamel underneath). With Flory, I had the whole wash and removal done in less than an hour, and not a single trace of paint on the sponge. It turned out beautifully. They have all kinds of different colors, including several different brown tones like the burnt umber Tojo suggested.