# Colour-code with classes

Give nodes, edges and groups a class to colour them, and add a legend that explains the colours.

## Why colour-code a diagram

Colour shows at a glance who does each step, or which system it belongs to. In this diagram, each colour is a role: Employee, Approver and Finance. The legend in the bottom-left corner names them.

![The expense approval flowchart with steps coloured by role: Employee steps in light blue, Approver steps in mid blue, Finance steps in dark blue. A legend in the bottom-left corner names the three roles.](/images/docs/diagrams/expense-approval.svg)

## Give a node, edge or group a class

A class is a name you give to the items that belong together. Line9 colours each class differently.

| To give a class to | Write                                              |
| ------------------ | -------------------------------------------------- |
| A node             | `pay["Payment in next payroll"]:::Finance`         |
| Several nodes      | `class pay,reject Finance`                         |
| A group            | `class finance Finance`                            |
| An edge            | `limit e1@--> director`, then `class e1 Escalated` |

Choose names your readers will understand, such as a team or a system: the legend shows them as written. A class name can't contain spaces, so use a hyphen, such as `Line-manager`.

With Line9 Pro, in the [Line9 editor](/docs/how-the-editor-works), put the cursor on a node, edge or group, or select several, and type `:class` followed by the name.

## The legend

The legend names each class and shows its colour. Line9 adds it once the diagram has a class, and places it in a corner of the diagram.

To hide the legend, click **Legend** in the style panel.

## How Line9 picks the colours

The theme sets the colours. Line9 ignores colours set in the text with `classDef` or `style`: only the class name matters.

- Classes take the theme's colours in the order they first appear in the text.
- Boardroom, Linen and Kingfisher have four colours for node classes. Edges and groups have colours of their own.
- A class sets only an edge's colour. Its line stays solid, dotted or thick, as written.
- A class beyond the theme's colours is drawn like an item with no class.
- An item with more than one class takes the colour of the first.
- The Blueprint theme draws every item alike, so classes don't change its colours.

## Next

- [Theme, orientation and spacing](/docs/theme-orientation-and-spacing): choose how the whole diagram looks.
- [Nodes, edges and groups](/docs/nodes-edges-and-groups): the parts you can give a class.