remove brown pillows. the above suggestions give you a blast of color. Add neutral colored window treatments that coordinate with wall color. I also like lee lee suggestions- would be a more subtle way of adding the color.

Do not add purple to that room. That would not make any sense. You already have your color palette established. Adding random colors should not be the goal. What you need to do is stick with the palette you already have. Color is not your problem. You need LAYERS. You need to build up that space so it's not so flat and one dimensional. You need an area rug. You need to upgrade the throw pillows. You're trying too hard to match the pillows to that piece of art work. Yes, keep the colors in the same family, but focus more on texture and then add pattern. All solid color pillows are too boring and flat. Then you need to pull that sectional away from the corner. Do not stick furniture in corners, that will never look good. Pull it into the center of the room and reconfigure it so that it is looking at whatever the focal wall is in the space. Without being able to see the entire space, maybe turn the couch so that it is looking at that blank wall that the long part of the couch is backed up onto now for example. in other words, get the couch into the center of the space on a large area rug however that fits best. Then get a console table to put behind the long part of the sectional with a large piece of modern sculpture art on it to go with your modern wall art.

No pops of color. And yes, "lose" the purple idea.

cpaul has a good point but if you changed just your art you could then add pops of color that would still give you a monochromatic look but with interest.

Karastan Euphoria Forfar Hazelnut Area Rug