Wambat.....That doesnt even look like the tyvek flashing too me.What i have always used is white. Tyvek flashing the sill material is different than the side and top material. Sill material goes on first...before installing the window. It is stretchy...It is applies to the inside sill then stretched over and down onto the tyvek. Next install window and put the side/top materialonto the side of the window..overlapping the tyvek. Then the top...you slit the tyvek so the top material laps the two sides and onto the sheathing. Then fold the tyvek back down onto the flashing and hold with the tape.