Color blindness test for kids: from what age and which test

Why test a child's colour vision at all

Inherited colour vision deficiency is present from birth and does not change, so finding it early is not about treatment: there is no cure. It is about understanding. A child who mixes up red and green crayons, struggles with colour-coded worksheets or calls a brown dog green is not being careless, and teachers and parents can adjust once they know. Early knowledge also avoids surprises later, for example when choosing a career where colour vision rules apply.

About 1 in 12 boys and 1 in 200 girls of Northern European descent have red-green colour vision deficiency. The rate is lower in many other groups; a large US preschool study found red-green deficiency in 5.6% of non-Hispanic white boys and fewer in other ethnic groups. In a class of 30 children, it is common for at least one child to be affected.

Signs that may point to colour vision deficiency

• Consistently naming colours wrongly, especially red, green, brown and orange, while knowing other words well.
• Choosing unusual colours when drawing: purple leaves, green skin, brown grass.
• Difficulty with colour-coded tasks, maps, games or sorting by colour.
• Relying on light and dark rather than on hue ("the dark one").
• A close male relative, especially on the mother's side, who is colour blind.

None of these proves anything on its own; young children are still learning colour names. They are a reason to test.

Why number plates do not work for young children

The classic Ishihara test needs the child to read and name digits. Many three- and four-year-olds cannot, and a child who does not answer can look like a child who cannot see the number. That is why tests for young children replace digits with simple shapes or pictures.

A well-known example is Color Vision Testing Made Easy (CVTME), a plate test with simple figures such as a circle, a star and a square. A study published by the College of Optometrists tested 98 children aged 15 months to 6 years and found that 75% of children over 3 and 100% of those aged 4 or more could understand and complete it.

From what age

Age	What usually works
Under 3	Formal testing is unreliable; watch for signs instead.
3-4 years	Shape or picture plates; the child can name or trace the shape.
5-7 years	Shape plates or number plates if the child knows digits well.
8+ years	Most adult tests, including number plates and arrangement tests.

How to run a check at home

1. Light and screen: test indoors out of direct sunlight. On a phone or tablet, turn brightness up and switch off Night Shift, True Tone and any colour filters.
2. Distance: hold the device at about arm's length, straight in front of the child.
3. Make it a game: ask "what shape is hiding here?" and let the child point or trace with a finger if naming is hard.
4. Do not prompt: avoid hints like "look, it's a circle". Accept "I don't see anything" as a valid answer.
5. Short sessions: a couple of minutes is enough. If the child is tired or distracted, try another day.
6. Repeat: if the result looks abnormal, repeat it on a different day before drawing conclusions.

Boys, girls and family history

Because the red and green pigment genes sit on the X chromosome, red-green colour blindness runs in families in a typical pattern. A colour blind father passes his X chromosome to all his daughters, who become carriers, but to none of his sons. A carrier mother has a one-in-two chance of passing the altered gene to each son. In practice this means a boy whose maternal grandfather or uncle is colour blind is at higher risk, and it is worth testing him even if you have noticed nothing.

Girls can be colour blind too, but much less often, usually when the father is colour blind and the mother is a carrier. Blue-yellow (tritan) defects follow a different inheritance pattern and affect boys and girls about equally, but they are rare.

Colour blindness at school

Teaching materials lean on colour more than most adults realise: coloured counters in maths, colour-coded maps and charts, "underline the nouns in red", red pen on green paper. A colour blind child can lose time or marks on tasks that test colour rather than knowledge. Once you know, a short note to the teacher usually solves most of it: label colours with words or patterns, use high-contrast pens, and avoid red and green as the only difference. Older children can also learn to use the colour names printed on pencils and the accessibility settings on tablets.

What the result means

A shape test at home is a screening, not a diagnosis. Screens vary in colour, and young children vary in attention. If your child misses shapes on more than one occasion, or you see the signs above, book a visit with a paediatric ophthalmologist or optometrist. They can confirm the result with calibrated tests and, when the child is older, determine the type and degree.

If your child is colour blind, practical steps help a lot: label crayons and pencils with names, ask the school to avoid colour-only instructions, and teach the child to ask when colour matters. Most colour blind children do well with these small adjustments.

A shape test on iPhone

Trichrome includes a test with large shapes for kids (test III) that does not need digits and looks at both red-green and blue-yellow. Before each test the app reminds you about brightness, Night Shift and viewing distance. It is a screening tool for a first look at home and does not replace an examination by an eye-care professional.