Answer:
The correct answer is b. Choose the Theme Colors command on the Design Tab.
Step-by-step explanation:
In Microsoft Office applications such as Word, Excel, and PowerPoint, users can modify the colors in a selected theme by choosing the "Theme Colors" command on the "Design" tab. This will open a drop-down menu where users can choose from a variety of pre-set color sets or create their own custom set. The other options listed in the question ("Choose the Theme Effects command on the Page Layout Ribbon," "Choose the Theme Effects command on the Home Ribbon," and "Choose the Theme Design command on the Page Layout Ribbon") are not the correct commands to modify theme colors.