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Here’s a post I never got around to finishing. Kind of surprising considering it’s a pretty simple concept.

Adobe Illustrator has a neat feature to automagically pick out inverse and complementary colours. Have you ever wondered how to do that in Photoshop or InDesign? It’s not that difficult. Here’s how I do it.

To get a complementary colour:

• Convert your colour into the Lab space.
• Invert the ‘a’ and ‘b’ values.

That is to say, if your is L: 61 a:-17 b:-46, the complementary colour is: L: 61 a:17 b:46

To invert the colour entirely, you only have to go one step further. Subtract L from 100, for example:

L: 61 a:-17 b:-46 becomes L: 39 a:17 b:46

That’s it! Happy colour-exploring.

Every now and again, I have to remind myself of the difference between additive and subtractive colour, and which colour mode, RGB or CMYK, uses which modal. The way I remind myself is with a simple rule called “which way to white.” It works like this:

Take a piece of paper that has been printed like an advertisement, presumably CMYK ink printed on a white sheet. How do you get the white colour? Take the ink away. Therefore, CMYK = subtractive.

RGB is therefore additive by deduction.

The result: CMYK = subtractive, RGB = additive, and “which way to white” helps you remember that.