You may hate this, but... have you thought of tea dyeing (which is staining, really) over it? If it is only the colors you want toned down that would dull the brightness. I once had a waaaaay bright tablecloth in similar colors actually, which I soaked in a pot of hot, strong tea. It was gorgeous once the colors were not so wildly vivid. I gave it to my daughter who adored it in its new form and who loved using it. However, this just screams little girl, so you could probably use it just about any way you want and have a child to love it whether you do or not.