Plan wall color. Use a color that enhances the shade of green in the sofa. Paint a wall directly behind the couch pale lime green, for instance, to blend with a bright green couch. Paint the wall white or cream if the couch is a darker green. Select wall colors you like, however. Don't choose the shade based solely on the sofa. Use colored pencils to sketch the color scheme as closely as possible to see what works.
Go over home design books. Look at examples of using furniture and accessories to blend with green shades in curtains or rugs, for example. Buy light oak end tables and a matching coffee table to tone down the color green. Paint a media cabinet a light parchment or taupe to harmonize with the green couch. Hang artwork with green leaves or green apples to tie in with the sofa. Frame the pictures all in glossy black frames.
Add an area rug to pull all colors together in the room. Buy a light brown tweed rug or a rug with bright colors used in throw pillows bought for the sofa. Purchase a dark purple area rug to match pillows with purple and lime stripes, for example. Choose a rug that will look appropriate from every angle in the room.
Use green plants in the room. Buy large indoor leafy plants or faux miniature trees to give the room a nature-look atmosphere. Place one or two potted vines on end tables near the green sofa. Add plants to make sure the green sofa finds a near-matching color in the room. Don't leave the sofa as a total green contrast to the rest of the room, or it will look out of place altogether.
Buy a large knitted throw or blanket to soften a green couch. Place a white fluffy throw across the back of a green sofa when the back faces into the room. Use this blanketlike accessory to tone down a huge section of the green if it's too bold for the space. Fold the throw to hang down to the bottom level of the sofa with only a small amount of green showing from the back view.