Today I learned about the Reveal.js available default themes.

NameEffect
blackBlack background, white text, blue links (default)
whiteWhite background, black text, blue links
leagueGray background, white text, blue links
beigeBeige background, dark text, brown links
skyBlue background, thin dark text, blue links
nightBlack background, thick white text, orange links
serifCappuccino background, gray text, brown links
simpleWhite background, black text, blue links
solarizedCream-colored background, dark green text, blue links
bloodDark background, thick white text, red links
moonDark blue background, thick grey text, blue links

Source