DFW CTLR EXPERIENCED OPERROR WHEN DEPARTING 2 ACFT ON SAME RNAV TRACK WITHOUT SUFFICIENT SEPARATION.

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MINIMUM STAFFING -- 6 FPL'S. WE HAD 4 FPL'S; 1 SUPVR; 1 DEVELOPMENTAL; NO TMC'S ON DUTY. 6 POS BEING MANNED BY 3 FPL'S AND 1 DEVELOPMENTAL -- AT TIME OF OPERROR. THE SUPVR WAS NOT IN CTL TWR AT TIME OF OCCURRENCE. 1 CTLR WORKING CIC; CD/FD; AND THE QUEUE -- 3 POS (COMBINED) -- 1 DEVELOPMENTAL CTLR (RECENT) WORKING LW-2; 1 CTLR WORKING GND CTL; I WAS WORKING LCL CTL W. THE DEVELOPMENTAL CTLR IS CHKED OUT ON GND; CD/FD; AND LW-2 (RECENTLY). I MOVED AN RJ OVER TO TXWY F; TXWY WH IN AN ATTEMPT TO SEPARATE THE RNAV TRACKS. I DEPARTED AN SLT; AND A GTH; THINKING THESE WERE DIFFERENT RNAV TRACKS. IN FACT; THEY ARE THE SAME TRACKS. I EXPECTED THEM TO DIVERGE AND THEY WERE ON THE SAME TRACK. I WAS UNAWARE THEY WERE THE SAME RNAV TRACK UNTIL THE TRACON CALLED THE TWR TO ADVISE THERE WAS A LOSS OF SEPARATION. THE PROB OCCURRED BECAUSE I WAS CONFUSED ON THE GTH BEING AN INSIDE TRACK (IN A S FLOW); NOT AN OUTSIDE TRACK. THERE ARE 16 DIFFERENT FIXES THAT APPEAR ON THE W HALF OF THE ARPT IF IT IS SEPARATED IN HALF. EACH OF THE 16 FIXES SHOW UP ON DEP STRIPS AND MUST BE INTERPED AS INSIDE OR OUTSIDE TRACK DEPENDING ON FLOW. THERE ARE 16 MORE FOR THE E SIDE OF ARPT; THAT MUST ALSO BE INTERPED FOR EACH FLOW. A QUICK WAY TO CORRECTLY INTERP THE FIXES AS INSIDE/OUTSIDE TRACK WOULD BE HELPFUL -- POSSIBLE STRIP MARKING IN DIFFERENT COLORED GREASE PEN -- BLACK 'I' FOR INSIDE - GREEN 'O' FOR OUTSIDE -- FOR EXAMPLE; TO PREVENT MISINTERP. STILL MUST BE MARKED CORRECTLY!