Ok I have some bad news people. I can’t help you turn this square into a solid color. The whole design of the square is in the color changes to make the heart. You could make it easily in a solid color and have a solid square with a rim of decorative stitches right near the edge.
The square is called Pixel Heart by Whistle and Ivy. I love it, and I am thinking of making it into a patch on a tote bag.