Making brown from red isn't easy. .....depending on the hues, red + green will give a greyish brown,........... red + black will give a dark reddish brown,............ Red + yellow to make orange then blue to get a true brown................................red + brown will give a reddish brown similar to mahogony....you could always add a little black to darken it.................all the above is by mixing pure colours of course,you never know how a fabric will react to dye.(or to re-dying)