I can't change anything around. What can I do to decorate?

Instead of painting walls, you could paint canvases in varying bright shades to liven up the walls.

Way to be respectful of people’s space! I would think that hanging your artwork would be find, particularly if you use something like the brand that shall remain nameless which rhymes with “a brand” adhesive strips that stretch. You could also bring plants in (if you have a green thumb) or change the lighting with a quirky lamp. In a few weeks, it will look like your own place.

Also adding little personal touches like brightly coloured throws and cushions can be fun.
I’m sure that your relative will be very happy that you are there. It will be a comfort to know she is not alone. I think it’s a lovely thing you’re doing. hugs xx

get rid of everything you don’t like, after that, your house will be half empty, if someone asks, you say your are in your “minimalist” phase :D

Can you hang your art on the walls? That would do a lot to make it yours. In addition, bright cushions, quilts and throws could bring in your palette.

Obviously, posters of me on the wall.

You could buy bedding that livens up or plays up the green. Knick knacks, lamps etc that are more your taste and just put her items safely away in a spare room closet. You can hang your artwork and the quiet green walls are pretty neutral.

@PretentiousArtist Or a collage of Fluther avatars. Riiiight above the bed.

I was also going to suggest throw pillows, throws, towels, and bright colored bed linens. I also agree with @galileogirl that you could safely store her things and add in items that are more to your taste. A suggestion if you do remove things to storage: take photos of how the rooms are before, and then use those to reconstruct her decorating scheme.

You might also consider storing your relative’s window treatments and putting in your own, or even getting some slipcovers for some of the upholstered pieces.

The green and brown sound quite nice – perhaps you could add in some orange and gold accents to bring things to life.

You can use fabric as wallpaper as a way to change the wall color without doing anything to the actual wall. There are a few way to hang it depending on the room. You can staple it along the top of the wall or the crease. You can also hang it on fish wire and attach the fish wire to the wall or if you can find a curtain rod long enough that would work too.

I second adding in some orange. Nice, bright, warm color that will work perfectly with the green. As far as making it feel like your home, don’t worry… your favorite books, pictures of people you love, and comfy bedding will do the trick in no time. :)

Brown and green are nature colors, so whatever you do with bright, bold colors will look good. Roll up the runner and put down a brighter colored rug, use colored artwork, framing everything in black with off white matting so it pops of the wall. Choose interesting lamps, bright colored bedspread, throw pillows, etc. You can put a lot of color into a neutral room.

Thanks guys, great answers! I’m going to go over there this weekend to see what I can do.

I am a little late (as usual) but some small rugs on top of the brown one would be good too and mobiles, I am a great fan of mobiles.

Embellish, ornament, and accessorize.