Abigail ClarkeAstronomers at the University of Warwick have announced what they describe as the first known green star, reported on 16 October 2026. The object is a cool white dwarf called WD J1330+6435, about 284 light-years from Earth, and its colour was worked out by passing its spectrum through a model of human colour vision. That last detail raises a question many readers are now asking: what does "green" actually mean when it depends on the eyes doing the looking?
What did the astronomers actually find?
According to Gizmodo's report on the study, the team led by Mark Hollands, with co-author Boris Gänsicke, both at the University of Warwick, analysed the star's spectrum. A spectrum is the fingerprint left when starlight is split into its component colours. The findings were published in the journal RAS Techniques and Instruments.
WD J1330+6435 is a white dwarf, the dead core of a star that has used up its fuel. Its surface temperature is roughly 4,000°C, cool by white dwarf standards. The researchers say it swallowed rocky material from its own planetary system, rich in calcium, lithium and sodium. Sodium in the star's atmosphere absorbs orange light, which shifts the overall impression towards a pale, ghostly green.
Nobody has looked at this star and seen green directly. White dwarfs are too faint and too distant for that, so the colour comes from modelling. The researchers fed the spectrum through a model of how human eyes respond to light and asked what a typical viewer would perceive. That makes this a story about physics and about perception in equal measure.
Why does a "modelled" colour matter to your eyes?
The phrase "a model of human colour vision" hides an assumption: that the viewer has typical colour vision. Human eyes detect colour using three kinds of light-sensitive cone cells in the retina. If one type is missing or works differently, the brain receives a different signal, and the same light can look different.
The NHS describes colour vision deficiency, often called colour blindness, as seeing colours differently from most people and having difficulty telling colours apart. It notes that the condition can run in families and that some people are born with it. It also says colour vision deficiency can sometimes be caused by eye conditions such as glaucoma, by other conditions such as diabetes, liver disease and multiple sclerosis, by an eye or head injury, by a stroke, or by taking certain medicines.
So the "green" of this star is the green a typical viewer would see. Someone with a red-green deficiency could see something quite different from the same light. The astronomers' result is robust as a statement about the light the star emits, but the label "green" is a statement about an average observer.
How do you know whether your own colour vision is typical?
Most people assume they see colours the way everyone else does, because they have never been tested. The NHS points out that colour vision testing is not part of the routine NHS eye test, although you can ask your optician for it if you think you or your child needs it.
There are two main tests, according to the NHS. The first is the Ishihara test, where you are asked to read images made up of coloured dots. The second is a colour arrangement test, where you are asked to put coloured objects in order of shade. The NHS adds that tests are available online, but that it is important to be checked by an optician if you have concerns about your vision.
Signs worth noticing include trouble telling similar shades apart, mixing up colours in clothes or charts, or finding traffic-light or wiring colour codes harder than other people seem to. A newly noticed change in colour perception in an adult deserves more urgency than a lifelong quirk, because of the medical causes listed above.
A concrete case: the 42-year-old who noticed colours "going flat"
Take a hypothetical reader, a 42-year-old who reads the green star headline and realises she has been struggling for around six months to tell the red and green indicator lights on her home router apart. She has never had trouble before. She also takes a new prescription medicine, started eight weeks ago, and has type 2 diabetes.
If this were a lifelong, inherited deficiency, the NHS says there is no treatment and most people adapt. But her case is different in one important way: the change is recent. The NHS lists diabetes and certain medicines among the possible causes, so the logical order of steps is as follows.
- If the change began after the new medicine, then ask the prescriber or pharmacist to review it. The NHS says that when colour vision is affected by medicines, changing them may help.
- If she has diabetes and the change is recent, then an eye examination matters sooner rather than later, because eye changes linked to diabetes are something an optician can check for.
- If both apply, then she should book an optician appointment within the next few weeks rather than waiting for her next routine test, and mention the timeline of 6 months and 8 weeks explicitly.
For her, a colour test takes minutes. For an adult with a sudden change, the real value is the conversation it starts about the underlying cause, not the test result alone.
Who should you consult, and when?
Which professional you need depends on the question.
- An optician or optometrist is the first stop for suspected colour vision problems. They can run an Ishihara or colour arrangement test and examine the eye for conditions such as glaucoma.
- A GP or specialist doctor is appropriate if the change might be linked to a condition such as diabetes, multiple sclerosis or liver disease, or if it follows a head injury or stroke symptoms. A sudden change alongside other symptoms should not wait.
- A pharmacist or prescriber can advise whether a medicine might be involved, and whether alternatives exist.
Parents have a separate reason to ask. The NHS advises going to an optician if you or your child have signs of colour vision deficiency. Children who struggle with colour-coded school materials sometimes go years without a diagnosis simply because nobody asked.
What does the green star teach us about everyday perception?
The Warwick discovery is a reminder that colour is not a property of an object alone. It is the result of light, a surface or source, and a visual system. When a researcher says a star is green, they are describing the output of that whole chain. When you say a traffic light is green, you are doing the same thing, with your own eyes as the final link.
For most people the chain works well. For some it does not, and the difference is easy to miss until something prompts a test. A headline about a distant dead star is as good a prompt as any.
What should you do next?
If you have ever wondered whether you see colours the way others do, or if you have noticed a recent change, the practical step is simple: ask an optician for a colour vision test and mention any medicines or conditions such as diabetes. If the change is sudden or comes with other symptoms, speak to a doctor promptly. The NHS has a clear overview of symptoms, tests and causes at NHS colour vision deficiency guidance.
You can find a health specialist on Expert Zoom to talk through a vision concern, and see how our experts handled a related eye-health question in our guide to eye safety during the August 2026 solar eclipse.
This article is general information, not medical advice. If you have concerns about your eyes or vision, consult a qualified optician or doctor.
