High Contrast

This is the only palette in the catalogue with a pass mark. Every other one is a matter of judgement. This one is measured: the Web Content Accessibility Guidelines put a number on the difference in lightness between two colours, and 7 to 1 is the level they call AAA for normal text.

The readers it serves are not a small group. Low vision, glare on a phone in sunlight, a tired projector and a third generation photocopy all take contrast away. A picture that starts at 7 to 1 survives all four.

Work in pairs, never in a list. The white on the near-black here reaches about 19.7 to 1. The yellow on the near-black reaches 15.4 to 1 and the cyan 13.7 to 1. The white on the deep blue reaches 9.3 to 1 and the yellow on it 7.3 to 1.

Drop the middle of the range. Mid greys are what pull a pair under the mark, so a high contrast set has a dark end, a light end and almost nothing between them.

Never let a hue carry the meaning alone. A shape, a label or a position has to say the same thing the colour says, or the message is gone for a reader who cannot separate the two hues.

Use it for signage, a warning, a slide read from the back of a room, a public information sheet, or anything that has to work on a phone outdoors.

Leave it alone when you want atmosphere. This palette has no quiet setting, and a picture that runs at maximum contrast everywhere gives the eye nowhere to rest.

Achromatic also runs from dark to light, but it promises nothing about a number. This palette is chosen against a measured threshold and checked.

Colour Blind Safe answers a different question. It keeps hues apart for a reader who cannot see one of them. High contrast keeps lightness apart for a reader who cannot resolve fine detail.

Road signs, fire exits and aircraft safety cards have run on this palette since long before the web put a number on it. The 7 to 1 figure is the AAA level in the Web Content Accessibility Guidelines. 4.5 to 1 is the AA level for normal text, and 3 to 1 is the floor for large text and for the edge of a control.

The model returns the right hues at the wrong lightness, usually a softened yellow on a mid grey. Say near-black and pure white, and say no mid greys.

Thin lines and small text arrive in the accent colour. A ratio is measured on the colour and not the size, but a hairline still disappears. Say flat areas with hard edges.