TRAVELING WITH A GERMAN "TWIN"PASS, CAN YOU USE THE PASS TO CROSS THE BORDER INTO FRANCE, SAY FROM BADEN-BADEN TO STRASBOURG, AND THEN AGAIN FROM COLMAR,FRANCE BACK TO BADEN-BADEN?
No. It's only good on the German side of the border.
The only places where you can go into another country from Germany with a German Rail pass are to Basel Badbahnhof, to Kufstein, Austria, to Salzburg, Austria, and between Pfronten, Germany, and Garmisch-Partenkirchen (on the Ausserfernbahn, through the Tirol), because all of those lines are run by German Rail.
Steve is right; those are short trips on French Rail and the fares are minimal. In both cases, the German Rail pass will get you to/from Kehl, Germany, just across the river from Strasbourg, and you can buy P-P ticket between there and France.