How to check the contrast in PowerPoint.

To find insufficient color contrast, look for text in your document that’s hard to read or to distinguish from the background.
If unsure, use the Colour Contrast Analyzer, a free app that analyzes colors and contrast, and displays results almost immediately.
To check that you have chosen the correct color contrast ratio, grag the Foreground eyedropper icon over a sample of your text or image of text. Drag the Background eyedropper icon over a sample of your background color. If the contrast ratio does not pass, then adjust your foreground or background until it does pass.