By 2019 Slack was a multi-billion-dollar company still wearing the logo it launched with — a beloved, and increasingly troublesome, hashtag.

Slack’s original mark was a colourful octothorpe — a plaid, hashtag-like “#” that users adored. In 2019, ahead of going public, Slack commissioned its first-ever rebrand from Pentagram, led by Michael Bierut. The new mark keeps the idea of the hash but rebuilds it from a cleaner set of shapes (a speech bubble and a lozenge), anchored by a confident aubergine. It’s a textbook example of evolving a loved logo without throwing away its equity — same idea, far better engineering.

The old logo wasn’t just busy — it was a production nightmare, and that’s the real story.

The original hashtag used 11 colours and had to be rotated at a precise 18 degrees; get either slightly wrong — a common occurrence across countless placements — and the whole mark looked broken. The 2019 redesign cut that to four accent colours in a fixed, forgiving configuration that works on any background, at any size, in a favicon or on a billboard. Bierut’s team also gave the mark proper clear-space rules and a single approved orientation, so it can’t be accidentally mangled the way the old one so often was. The lesson is one every designer eventually learns: a logo isn’t finished when it looks good in the presentation — it’s finished when it survives the real world, in the hands of people who’ve never read the guidelines.

One deep, distinctive anchor colour, plus four brights that keep it playful. Click a swatch to copy the hex.

Aubergine (#4A154B) is Slack’s anchor — a rich, unusual purple that few brands own — and it carries the wordmark and most surfaces. The four accents — blue #36C5F0, green #2EB67D, yellow #ECB22E, red #E01E5A — bring the energy, living inside the mark and across illustrations. It’s a smart split: a serious, ownable base colour for recognition, with a lively supporting cast for warmth.

Slack’s type is quiet on purpose — a clean grotesque that lets the colour and voice do the talking.

For its brand and marketing, Slack leans on Larsseit, a crisp geometric grotesque that pairs neatly with the aubergine and keeps headlines calm and legible. Inside the product, the long-serving humanist sans Lato carried the interface for years. The division is familiar by now: a distinctive display voice for the brand, a neutral, screen-tested workhorse for the software — so the app never fights the marketing, and vice versa. It’s a deliberately restrained choice for a product whose whole job is to get out of the way and let people talk.

Slack’s identity was never only visual — its tone of voice did as much brand-building as the aubergine.

Long before the 2019 rebrand tidied up the logo, Slack had already made itself recognisable through how it talked. The product’s onboarding, empty states and error messages were written to feel like a considerate colleague rather than a machine — friendly, lightly witty, and relentlessly plain-spoken. That tone reached its most famous expression in the mascot bot, Slackbot, and in loading messages and notifications that treated the user as a person having a busy day. For a piece of enterprise software, sounding human was a genuine differentiator, and it made the brand feel warm in a category better known for grey dashboards.

The visual system was built to carry that voice rather than fight it. The playful four accent colours give illustrators a lively kit for the small spot drawings that pepper the marketing site and the app, while the steady aubergine keeps the whole thing feeling grounded and premium instead of childish. Slack even codified its principles into a widely shared idea — that the software should reduce the friction of work, summed up in the promise of being “where work happens.” When Salesforce acquired the company in a deal valued around $27.7 billion, that personality survived largely intact, a sign of how much equity lived in the tone and the colour rather than in any single logo. It is a reminder that a brand is the sum of every touchpoint — the words as much as the marks — and that consistency of character is what makes an identity feel like a place rather than a product.

Keep Slack’s identity on hand — save it to a board in the Made Good inspiration library.