In ty­pog­ra­phy, color is a term with two meanings.

First, ty­pog­ra­phers will some­times speak of a font as cre­at­ing a cer­tain color on the page—even when it’s black. Used this way, the word en­cap­su­lates a set of hard-to-quan­tify char­ac­ter­is­tics like dark­ness, con­trast, rhythm, and texture.

The sec­ond mean­ing is the usual one—color as the op­po­site of black & white. This was once an ir­rel­e­vant topic, as most of us had to be sat­is­fied with mono­chrome laser print­ers. These days, color print­ers are ubiq­ui­tous and more writ­ing is de­liv­ered on screen. So color has be­come a prac­ti­cal consideration.

1. On a page of text, noth­ing draws the eye more pow­er­fully than a con­trast be­tween light and dark col­ors. This is why a bold font cre­ates more em­pha­sis than an italic font. (See also bold or italic.)

2. The per­ceived in­ten­sity of col­ored type de­pends not just on the color, but also the size and weight of the font. So a thin or small font can carry a more in­tense color than a heavy or large font.

3. I’m not say­ing it can never be done well, but when some­one puts col­ored type on a col­ored back­ground, I usu­ally wish they hadn’t.

body text in printed doc­u­ments (e.g., ré­sumés, re­search pa­pers, let­ters) must al­ways be set in black type. No exceptions.

At a typ­i­cal body-text point size, color isn’t ef­fec­tive as a form of em­pha­sis. Small let­ter­forms don’t cover much sur­face area on the page, so col­ored text isn’t no­ticed un­less it’s loud.

Pro­fes­sion­ally printed doc­u­ments (e.g., let­ter­head, busi­ness cards) can in­clude text set in color, but use it ju­di­ciously. Mul­ti­ple shades of one color are usu­ally bet­ter than mul­ti­ple con­trast­ing colors.

The horse may be long out of the barn on this one, but on the web, the same rule of re­straint ap­plies: less color is more ef­fec­tive. When every­thing is em­pha­sized, noth­ing is emphasized.

Con­sider mak­ing your text dark gray rather than black. Un­like a piece of pa­per—which re­flects am­bi­ent light—a com­puter screen projects its own light and tends to have more se­vere con­trast. There­fore, on screen, dark-gray text can be more com­fort­able to read than black text. That’s why many dig­i­tal-book read­ers let you re­duce the screen bright­ness or change the text color.

Color re­mains the id­iomatic way to de­note click­a­bil­ity on the web. So feel free to use color (with or with­out un­der­lin­ing) for hy­per­links. But be care­ful us­ing it on non-click­able text, as it may con­fuse readers.

PDFs are read on both screen and pa­per, so which set of rules you fol­low de­pends on how you ex­pect the PDF to be used. If there’s a rea­son­able chance the PDF will be printed, don’t bother with dark-gray body text—it’ll look gritty and strange when printed.