Create a plan for your room. Decide on the style of the room, as well as how elaborate or subtle you want the furnishings and decorations to be.
Decide on wall color. You could opt to paint the walls in sage green with white trim along the door frame and baseboard. Sage is considered a restful tone, so it is much better suited for a bedroom as opposed to a vibrant, energetic yellow. Buttery yellow tones or soft yellows are appropriate for accent walls in bedrooms and living spaces, but may clash with an opposing sage green wall. It's best to paint your walls one or the other, to avoid a "busy" or "cluttered" look.
Choose color accents. If your walls are sage, soft pastels and buttery yellows create a comforting country appeal, whereas soft yellow walls with sage green accents adds a complementary warm glow. Green tones help to harmonize the energetic feel of yellow hues, which creates a relaxed, yet cheerful atmosphere.
Pick matching furniture for your theme. White will bring both sage and yellow together, whether it's in a pure white comforter set or a white sofa and loveseat. If you're unable to afford new furniture, white slipcovers for your sofa and loveseat will suffice.
Mix and match soft shades of green and yellow, along with a few bold and vibrant pieces. Throw pillows, vases, candles and picture frames are decor pieces that will liven up the room. Sunflower yellow and bright grassy green should be implemented in small amounts to avoid going over the top.