What you have is neutral so the possibilities are endless. Do you have any other objects such as art or rugs with color to pull inspiration from. I would consider blues, oranges, lime green, or other neutral colors. Look around on the internet, there is a ton of inspiration out there. If you decide on a color let us know and we can help you from there.

I agree with carminnc you have a great base here - the color wheel is your oyster! But, like you I have an obsession with orange and chevrons (I use both for my blog website banner!) if you like chevron but want to maintain the use-ablity of all your pieces so you can easily change your accent color in the future you could consider a chevron ottoman instead of chair (cheaper!).

pillows in an ikat chevron would be a modern take on the usual chevron pattern and are "on trend"...

Here is a link that might be useful: orange accents

I think a light creamy linen would look great on the windows or you could always match the walls too. Either way would be super. That way you can introduce a few pillows with a cream in them and pop the cream color around the room. I love the idea of the orange but, as the others say, you have a wide choice of colors from which to choose. Your choices so far are spot on and gorgeous.