Contrast and colour on slides: a readability guide

You can get the words, the structure and the font size right, and still lose your audience at the first slide because nobody can read it. Colour and contrast are often the reason. The good news is that they’re among the easiest things to fix, once you know what to look for.

What contrast means on a slide

Contrast is the difference in lightness between text and whatever is behind it. Dark navy on white has strong contrast. Mid-grey on light grey has weak contrast. Notice that it’s about lightness, not hue. Red text on a green background can be two very different colours and still be hard to read, because both are similarly dark.

Here’s the part that catches people out: your laptop screen is probably the best place your slides will ever be seen. Projectors wash colours out, meeting-room lights fade them further, and a shared screen on a video call compresses them. A pairing that looks crisp on your screen can turn to mush on the wall. So aim for more contrast than you think you need.

Pairings that work, and ones to avoid

Some safe starting points:

Works well	Why
Near-black text on white or off-white	Strong contrast, comfortable to read
White text on a dark navy or charcoal	Strong contrast, works in dim rooms
Dark text on a pale tint of your brand colour	Keeps the brand, stays readable

And some that often cause trouble:

Be careful with	What tends to happen
Light grey text on white	Disappears on a projector
Red on green, or green on red	Hard to separate for many viewers
Saturated blue text on black	Looks vivid on screen, hard to read in a room
Text over a photograph	Parts of the text land on light areas, parts on dark
Yellow text on white	Almost invisible from a distance

Choose a small palette and stick to it

Most readable decks use very few colours:

• One background colour, used on almost every slide.
• One main text colour, with strong contrast against that background.
• One accent colour, for the thing you want people to notice.
• A neutral grey, for less important elements like axis labels or footers, still dark enough to read.

If your brand palette has six colours, you don’t need all six on every slide. Pick the accent that works best against your background and save the others for charts.

Use colour to point, not to decorate

The accent colour is your pointer. Use it on the one number, word or bar that carries the slide’s message, and leave everything else neutral. When everything is highlighted, nothing is.

For example, on a chart comparing five regions, colour the region you’re talking about in your accent and the other four in grey. The audience’s eyes go straight to the right place, and your title can tell them why it matters. Chart design for slides covers the rest.

Don’t rely on colour alone to carry meaning, though. Some people in your audience may not be able to tell certain colours apart, and a faded projector can make two colours look the same. Pair colour with a second cue: a label, a pattern, a position or a bold weight. “Target met” written next to a green tick is clearer than the green tick on its own.

Text over images

Photos make slides feel alive, but text placed directly on a photo is one of the most common readability problems. Bright skies, white shirts and busy backgrounds all fight with your words.

You have a few options:

1. Put the text beside the image, not on it. Split the slide into a picture side and a text side.
2. Add a solid block behind the text, in your background colour.
3. Darken or lighten the whole image so the text has an even surface to sit on.
4. Choose a photo with a calm area and place the text there, then check it at full screen.

Option one is the safest. Check the others on the real screen.

Dark slides or light slides?

Both can work. Light backgrounds suit bright rooms and printed handouts. Dark backgrounds can feel calmer in a dim room or on a big stage.

What matters more is consistency. Switching between light and dark slides throughout a deck makes it feel jumpy. If you want a change of pace, say for section dividers, do it deliberately and keep the pattern the same throughout.

How to test your colours

You don’t need special tools to catch most problems.

The squint test. Step back from your screen and squint. Text that blurs into its background will vanish first. That’s the text to fix.

The greyscale test. Temporarily turn your slides to greyscale, or print one in black and white. If two colours that mean different things become the same grey, add a second cue.

The brightness test. Turn your screen brightness right down and flick through the deck. It’s a rough stand-in for a washed-out projector.

The real-room test. If you can, run the deck on the screen or projector you’ll actually use, and look from the back row. Nothing beats it.

A quick colour checklist

Before you present, check that:

• every slide uses the same background
• body text has strong contrast against it, including on a dim screen
• you’ve used one accent colour, on purpose
• nothing important relies on colour alone
• no text sits directly on a busy part of a photo
• greys used for labels are still easy to read
• the deck passes the squint and greyscale tests

Colour works alongside size and spacing. For the other half of readability, see font size rules for readable slides.