The colour of sheer fabric changes with age. Sunlight bleaches the fabric, time yellows it and pollutants in the air stain it. A brand-new panel will not match the older panels, so it is difficult to replace just one sheer panel. Replacing all the sheers can be expensive, especially if the room has multiple windows, so it is worth the effort to repair rips in sheer curtains. Seams in sheer fabric are always visible, but you can repair ripped sheer curtains by adding new seams and removing the damaged sections.
Take down the ripped sheer.
Fold the sheer from top to bottom along the centre of the rip. Fold the right sides of the fabric together. Be sure the top and bottom edges of the curtain are even so that the fold is straight up and down.
Pin the fabric together 1/4 inch from the edges of the rip. Pin the fabric in a straight line from the top to the bottom of the curtain.
Use a straight stitch to make a seam in the fabric along the line of pins.
Cut the seam allowance to 1/2 inch and finish it with an overcast stitch. You will be cutting off the ripped section. If the rip was small you may not have to cut any fabric off or finish the edge.
Use a low iron and a press cloth to press the seam open and rehang the sheer.