# The colour is the warning; the picture is the detail

> A dashboard warning lamp key runs eight pictograms in four colours. Red means stop now, amber means look into it, and blue and green mean nothing is actually wrong.

August 19, 2026 · https://justog.club/stories/handbook-warning-lamp-key

Eight symbols in a column. An oil can, a battery, a thermometer sitting in water, a handbrake —
red. A triangle with an exclamation mark, a fuel pump — amber. A headlamp — blue. A pair of arrows
— green.

Nobody needs to have opened the handbook to know which three of those eight mean pull over now.

## What is a warning lamp key actually organised by?

Colour first, symbol second — the reverse of how it looks at first glance.

Eight different pictures, drawn small and plain, would ask a driver to have memorised eight
separate meanings. Four colours ask them to have memorised one scale: red, amber, blue, green. The
symbol tells you which system is involved. The colour tells you how urgently you need to care, and
it's the colour a driver reads first, from across the cabin, before the picture registers at all.

## Why do oil pressure, charge, coolant temp and brake all share the same colour?

Because each one, ignored, can end in the same kind of outcome — damage that gets worse the longer
the vehicle keeps running.

Lose oil pressure and the engine can seize. Overheat the coolant and the same thing can happen by a
different route. A charge warning means the battery is no longer being replenished. A brake warning
means the system meant to stop the vehicle isn't fully able to. None of the four share a mechanism,
but they share a consequence, which is exactly what red is for on this key — not "this system",
but "this can't wait".

## What's the difference between amber and red here?

Amber means something needs attention; red means the vehicle needs to stop.

The general warning triangle and the fuel lamp both sit at amber, because neither demands an
immediate halt — a low fuel warning wants a fill-up soon, not a stop on the hard shoulder, and the
general symbol is usually a prompt to check the handbook for what else is lit rather than an
emergency on its own. Amber is the lamp asking for a decision at the next sensible opportunity, not
this instant.

## Why are main beam and indicators a different colour again?

Because blue and green aren't warnings at all — they're confirmations that something the driver
switched on is doing what it was told.

Main beam in blue and indicators in green tell the driver a function is currently active, nothing
more. Reading them on the same scale as the red and amber lamps would be a mistake the colour is
specifically built to prevent: green next to red, at a glance, already says one of these is fine
and the other isn't, before either symbol has been read.

## Who owns a colour convention like this?

Nobody owns red meaning stop or green meaning fine — that convention predates any one vehicle and
is shared across the whole trade, the same way
[a wire's colour carries no owner either](/stories/wiring-loom-colour-code).

What's owned is a manufacturer's own drawn set of symbols, their exact linework and the handbook
page they sit on — licensable if reproducing one specific book is the point. Drawn fresh, plain and
generic, the key keeps the convention and owes nobody a badge.

## Does this only make sense on a dashboard?

The logic generalises anywhere a mixed audience has to judge urgency without training — a fixed key
where colour carries the verdict and the symbol carries the explanation works the same way a
[tyre pressure plate solves urgency with a single instruction rather than a lecture](/stories/tyre-pressure-door-plate).

## Does it print well?

Yes — flat pictograms in a fixed set of colours are close to ideal print artwork.

Keep each symbol simple enough to read at a glance, the same restraint the real lamps are built
under, and hold the four colours to exactly this scheme rather than inventing a fifth for variety —
the whole point of the design is that there are only four meanings to learn. Black ground lets all
four sit at full strength without any of them fighting the others for attention.

## How do I get one made?

Describe your key at [JustOG](/) — which eight lamps, and which colour each one carries. Pick a
direction, drag the crop frame, see it composited on the real garment, and it's made to order and
shipped.

Designs other people have published are in the [shop](/shop).

Eight symbols, four colours, and the whole system readable before a single word of the manual.