Thank you for your comment, any feedback is appreciated. There are a few problems with your suggestions though, so I hope you won't mind if I point one out. This is a watercolor painting so working with grey won't work to desaturate the background. In fact there is no real grey watercolor as most of those colors are simply variants of black. The most famous is payne's grey which is translucent black intermixed with blue and sometimes green - depending on the recipe. Adding any variation of black to a watercolor painting will make the colors muddy and darker, so it's the opposite of the effect you've described. The solution would be to use white, but unfortunately I have my doubts that my Titanic White is up for the job. Another way could be to try and lift the color up from the painting, but that rarely works with the kind of paper I'm using after the paint has dried for more than 24 hours (I'm using Canson Arches Aquarelle paper hot pressed).
But I'll be sure to keep your advice in mind for further paintings.