Final answer:
To make the text take on the color of the underlying image in a layer style, you should set the Fill opacity to 0.
Step-by-step explanation:
To make the text take on the color of the underlying image in a layer style, you should set the Fill opacity to 0. This will make the content underneath the text visible through the layer style. By setting the Fill opacity to 0, the text will blend with the color of the image. This is the correct option to achieve the desired effect.