The colors of the grade pills can be modified for the entire instance. We can choose colors and the values at which each of them is displayed or completely remove the colors.

To configure the colors, go to Admin Panel > Courses > Course Settings and click Gradebook Settings.

First select whether you want colored grade boxes or colorless. If you choose colorless, all will be dark gray with the grade in white. 

If you select colored boxes, you will be able to select the percentage range and the color corresponding to each one. 

You can add or remove rows with the buttons + and x and change the color by selecting from the dropdown.

When you finish configuring the colors and ranges, click Submit to save and you're done.