What if your image has no quiet space for you to place your text over? What if, no matter what font color you choose, there is not enough contrast between your text and the background to make your font readable? For example, consider the following slide:
In the slide, the picture is too busy, making it difficult to achieve sufficient contrast between the text and the image.
One option to achieve better contrast is to fill the text box with color. For example, we could fill the text box with a black background.
Another technique you can use is to fill the text box (or shape) with a solid color but to make it semi-transparent so that the background is partially visible. You can see an example of this below:
To make a text box (or shape) semi-transparent, go to Format Shape >> Fill >> Transparency. Use the transparency slider to make your shape as transparent as you wish.