Every identity must first work in solid black and white (1). There are too many situations to ignore where this constraint is a reality. Newspapers and the Yellow Pages don’t do well with halftones, especially when the size is small. Businesses often print forms in black only, and some businesses have many forms. A solid black-and-white original will always reproduce better in photocopies and faxes than a color one.
Besides, as was mentioned in previous chapters, when color is allowed to dictate designs, it can be a distraction that allows esthetically inferior forms, proportions and shape refinements to slip by unnoticed, at least initially. Sooner or later, however, shoddy work will be recognized for what it is.
Unless an identity is a wordmark, it will be made up of a monogram or logo and a signature. Both elements together, not the logo alone, make up the identity.
Signatures should always get the greater contrast (2). This may seem counter-intuitive, because the logo typically takes much more time to design than the signature, but this rule remains valid. Why? Because the signature must be read. A logo is useful only if a viewer has seen it before and has learned to associate it with a company. On the other hand, if the signature can be read, it has communicated, even for a first-time viewer. This is true with both positive and reversed versions of an identity (3); the signature still receives the greater contrast.
The vast majority of identities use a black signature to assure readability. And black gives the maximum contrast on white backgrounds. This might inspire the unwise to seek some other color for the signature “just to be different.” But any reason to use some other color than black must be really crucial to not be a bad bargain in the long run.
Even if an identity has a color logo and a color signature, the signature should have no less than a 60% contrast with any background (4). A logo may have less contrast than a signature, but never less than 40%. This provides a natural hierarchy in the identity in terms of contrast: first the signature and second the logo.
Color can be an important part of an identity, and every logo should be able to work in some color (5). When applying color, the signature still gets the greater contrast, whether the identity is used positive or reversed (6).
But remember this inescapable fact: a color is also a value. A medium-red could be equivalent to a 50% gray, and might be used equally well as a positive or reverse identity (5, 6).
Since a signature needs at least 60% contrast, it is absolutely impossible to achieve that on a 50% gray background. Also, a mid-value background will almost always kill the contrast with a logo (7). Therefore, mid-value backgrounds should be avoided wherever possible. When this is not possible, the only viable solution is to use an all-white identity (8).
If the color of a logo is darker than 60% in a positive identity (9), it will not work in reverse (10).
One alternative is to use an all-white identity reversed out of the corporate color (11).
But for true reversal versions, many companies employ an alternative corporate color. It should not be just a tint of the original color (12) as the color will feel washed out. This is because white is totally neutral, and making a tint of any color naturally desaturates it. A less saturated color will have a different emotional impact compared to the original color.
An alternative reverse color version should keep the same degree of saturation, even if the hue is adjusted a bit to achieve an appropriately lighter value (13).
Adapted from Logo Design Theory: How Branding Design Really Works