The title says it all Besides that, it would be nice if you were able to specify the character with which invalid ones get replaced, I would prefer "_" e. g. instead of " ".
Fixed in r1294180 and r1294186 Colon is escaped and there is a WorkbookUtil.createSafeSheetName(final String nameProposal, char replaceChar) method that allows you to control replacement of invalid characters. Yegor