You can change the color of text to any color you want using the Pixelmator Pro color picker or the macOS Colors window.
Select the text you want to change.
To change all of the text in a text box, select the text box.
Click the color well in the Tool Options pane to choose a color or click to open the Colors window.
You can also customize the look of text (change the fill color, add stroke, or shadows) using layer styles.