Lots of nice features in your pretty kitchen, but I think you are right - some color would be good. I think you can choose anything light that you like - depends on colors in any adjoining rooms / spaces. Do you have pretty table linens that you see from the kitchen? I'd go with greens, blues, even red - jazz it up with what you like! Curtains or even Roman shades that sit a little higher on the window would make it brighter, too - the curtain you have seems too long to me.

The valence is too big - does the sun shine in? I’d go for something that is skinnier at the top and drapes down the sides, or leave it naked and hang some pretty colored glass decoration. And a pretty rug will help. Nice kitchen btw!

I agree with V K about adding almost any color and hanging either a straight valance or Roman shade. If you sew, this would be a very simple project, and there are tons of fabrics and colors to choose from, especially online at fabric.com. Here are a few examples, but, with your great basics, a bit of color will put the finishing touch on your space.

No ruffled valances please. As just above is nice.

I do not have curtains on my kitchen window. Privacy is not an issue. Something for you to consider.

I made a faux roman shade - looks like a roman shade but doesn't actually go down. If you can sew a little, it is a simple project.

https://www.houzz.com/photos/my-pics-work-in-progress-phvw-vp~110720042

Here is a picture of my living room. It's from a different angle but this is colors you see from the kitchen. This was taken at Christmas.