During the transition period (until around the end of September, 2015) the old color styling will also be available for older pages.
During the transition period, if you want to change both old and new pages to the same color style, you will need to set it up in both the old and the new color setting in the Widget Style page. Come October, you will be able to set effectively all of your page colors in the new color scheme editor.
If your current colors are all set, you will not need to do anything. The old color scheme will continue to work.