You'll be surprised as to how different your sofa will looks once you add the coffee table, art work, lamps, etc. Have your purchased these pieces yet? You are absolutely right about the effect of light on colors. Have you tried changing out your lightbulbs? In my home I have a lot of smaller light fixtures (can light on the floor lighting up, torchiere, table lamps, accent lamps). With some I put in different colored light bulbs (incandescent for the yellow, soft pink for a warm glow, a blue in the can light) to balance the colors overall in my room. Have fun experimenting with the colors of light, and how it can impact your room.

When I look at the gray pillows on the couch, it makes the couch look more gray to my eye. When I look at the more taupe-ish pillows on the couch, it makes the couch look more taupe. I think the trick here is to stick to gray fabrics around the couch and it will look gray. What a cool sofa, by the way. I like what you're starting with.

Add a large modern-patterned rug which includes your gray color will bring the sectional to life and suggest colors for chairs, art, and accent pieces.

Thank you so much everyone! You seriously made my day! I haven't purchased the rugs, coffee table or arts, yet. Also, I haven't tried different bulbs. But definitely will go with the ideas above.

It's my first time decorating a house, so I get little anxious time to time to achieve to look I want. So, thank you again! :)

The wall colour is not the best choice, looks green to me but everything will improve once you add the rest of the furniture and accessories.

Do you have an after photo? Would love to see what you came up with ! :)