Consider the following physical description in Hamnet, the Folger’s online catalog (it’s for an edition of Anna Jameson’s Characteristics of women, also published as Shakespeare’s heroines):
xl, 340 p.,  leaves of plates : col. ill. ; 28 cm.
The first part translates as “the printed portion of this book consists of 40 pages numbered with sequential roman numerals followed by 340 pages numbered with sequential arabic numerals, plus 12 unnumbered plates at some unspecified location or locations amongst those pages.” The second part, after the colon, translates into the vernacular much more succinctly: “col. ill.” means that the illustrations are in color. Here’s an example:
The great thing about the mandatory abbreviation “col.” in the physical description field is that it avoids the need to pick sides in the color/colour spelling divide, an important feature for a shared set of cataloging rules that had to gain official approval from representatives of Australia, Britain, Canada, and the United States. ((That it helps the description fit on a 3 x 5 inch card was once a great thing, too. Now it’s a footnote for history buffs.))
Unfortunately, though, the abbreviation “col.” obscures an important distinction for the material history of the book: is it a color illustration, or a colored illustration? In other words, is the color inherent in the image, or was the color applied to an existing image after manufacture? For a common household example, think of a family photo album with black-and-white photos from the 1940s and color photos from the 1980s, but perhaps also colored photos from the 1940s in the form of hand-tinted black-and-whites.
The “Lady Macbeth” illustration shown above happens to be from a copy of Characteristics of women with colored illustrations. The engraving was printed in black ink, then colored by hand (probably a mix of stencil painting and free-hand).
Plain versions of the same engraving also exist:
Under magnification, it’s clear that the engraved lines and dots in the colored engraving are black. What’s less clear without experience is that the color has been hand-painted on top of this base image, not printed. Compare the same detail of the wrist area from the two copies:
On the left, green, yellow, orange, and pale peach have been painted over the black design lines, making this a more luxurious version of the book. (Confession: although this pairing makes the point about color, it’s not a perfect comparison because the uncolored copy is, in fact, a later state of the illustration, with diagonal lines added to the dress). ((Different “states” of the same print are the result of deliberate changes to the printing plate, regardless of how much time has elapsed. Prints made several years apart from an unaltered plate are the same state; prints made several years apart where the publisher’s name was the only thing altered on the plate are different states; prints made the same day from a plate that had a few lines and squiggles added or burnished off are different states. Bibliophiles will have noticed that this is not what “state” means in book printing. The meanings of “edition” and “impression” are also examples of art historians and book historians being separated by a common language, but this footnote has gone on long enough.))
A color illustration, on the other hand, is printed in color, and requires either multiple runs through the press (one for each color) or careful inking of the plate in multiple colors before each run through the press. The latter, known as à la poupée printing (from the French term for the dabbers used to apply the ink) is uncommon in bookwork because it is so labor-intensive compared with hand-coloring. When you look closely at an à la poupée engraving, you can see that the dots and lines themselves are in different colors, not black or dark brown with the other colors painted over later:
Most color illustrations are printed from multiple runs through the press, not à la poupée, however. Two-color printing is relatively familiar to readers of early modern books thanks to examples of title pages printed in red and black:
The more colors added, the more difficult it is to keep the registration correct so that the printing plate for each color lines up correctly on the paper. Even the simple two-color title page shown here has the publisher’s name mis-aligned in the space left for it at the bottom. It was not until technological improvements in the 19th century that color printing overtook hand-coloring in book work.
Here’s a detail from another color print of Ophelia, this time printed from multiple lithographic stones, each contributing a separate layer of color. The registration is very good, though in my opinion the lithographer shouldn’t have tried to make purple by layering red and blue in the flowers. It just comes out brown.
As for my original gripe about cataloging rules obscuring the difference between a color print and a colored print by mandating use of an abbreviation, I’m happy to say that “col.” is on its way to being a thing of the past because the next generation of cataloging rules avoids abbreviations. RDA: Resource Description & Access, which is replacing Anglo-American Cataloguing Rules, 2nd ed. rev. (currently used at the Folger for books published after 1830) says only “record the presence of colour using an appropriate term” followed by non-prescriptive examples of such terms (including both “colour” and “color”). Will Descriptive Cataloging of Rare Materials (Books), the rules used at the Folger for earlier books, follow suit? This is currently being studied by the DCRM-RDA Task Force. My hope is that the revised rare materials cataloging rules will suggest “color” and “hand-colored” in the examples, since it’s easier to grasp the nuance of “colored” when it’s used in a phrase.