fix style sheet color lost after open and save

Created originally on Bitbucket by 王 强

Changesets for this Pull Request have not been imported, because it had been already declined on Bitbucket. Marked as closed by the import user.

same as https://bitbucket.org/openpyxl/openpyxl/pull-requests/378/fix-style-sheet-color-lost-after-open-and/diff