BASIC PRINCIPLES FOR USING CONTRAST
Use contrasting colors for clarity and visual interest. If it’s a different color, it should be obviously different.
Make the most important thing on the document the biggest and boldest. Use clearly different sizes for fonts and icons. If they’re meant to be different sizes, they should be significantly different.
Use different font families when using more than one font. Contrast serif body text, for example, with a sans serif or script heading. If they’re different typefaces, they should be very different.
Highlight no more than 10% of objects on a document. Make headings and important text and objects stand out by using boldface, color, italics, underlining, reverse type, and so forth. Only use two or three techniques at once and don’t use ALL CAPS to highlight.
When overlaying text on top of an image or watermark, contrast the background with the text significantly to avoid conflicts or visual noise.