1) Click on the Themes button in your account's main navigation.

2) Click on the + Create Theme button (or click on one of the themes you've already created).

3) Find the Custom Colors section and click Enable.

4) Find the area or text on the form where you would like to change the color. Either copy and paste a color's hex code into the corresponding field or click on the field and choose from the unlimited color palette.

5) Once you've made all of your color selections, click the Save & Finish button.

6) Now, when you create a payment form, you can apply this theme design to the form.