Online / Website
For accessibility for all readers, avoid fonts with serifs (the decoration added to letters to make them pretty). One of the most universal fonts, without serifs/sans-serif, is Arial.
For presentations on a computer (kiosk mode) any color combination with enough contrast is acceptable. Visually though, keep the background colors muted and the font contrast high.
Background images, as pictures, are often distracting rather than helpful. If you wish to use a background image, increase its transparency (make it more see through). Do not use text in the background. For accessibility purposes that text cannot be read by a screen reader.
Citations in a Presentation
Under images or after quotations, include an in-text citation with just enough information to point the reader to the correct entry in the Works page.
All citations should point to entries in a Works page at the very end of the presentation.
PowerPoint, Slides, Sway, or Similar Presentation
Most presentation software will have a theme. Pick a theme in which the fonts are legible from a distance. For accessibility purposes avoid fonts with serifs (the decoration added to letters to make them pretty) or that look like handwriting. Pick a font without serifs; Arial is one of the most common.
For a typical classroom, 16 point is the smallest size you would want to project. Anything smaller and it is too small to read from a distance.
For presentations in a room try to make the background match the color of the room behind the screen. The font color should stand out / be in high contrast with that color.
Background images, as pictures, are often distracting rather than helpful. If you wish to use a background image, increase its transparency (make it more see through).
Presentation software is meant to be visually stimulating. An effective presentation will often have less than 100 words. Four pictures that make statements and move the speaker to address the image has more power than 20 slides of text.