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Created attachment 72490 [details, diff] eix-0.5.0_beta-force-color-opt.patch
diff-eix also has a --force-color options, perhaps that should be patched too? Btw, you didn't update --help and the manpage.
Created attachment 72855 [details, diff] eix-0.5.0_beta-force-color-opt-r1.patch
fixed in 0.5.0_pre1