How to Make a DIY Colour Mixer at Home: A Fun STEM Activity for Kids This Summer

What if your child could hold a science experiment in the palm of their hand? This summer, My Stem Lab is helping kids discover the magic of colour mixing — not on a screen, but with their own hands. In this post, we'll walk you through how to build a DIY pocket colour mixer using simple materials, and explain the real science behind why colours combine the way they do.

Whether you're a parent looking for screen-free summer activities, a teacher planning hands-on STEM lessons, or simply a curious kid who loves creating things — this activity is for you. It takes about 30 minutes, costs almost nothing, and leaves children with a reusable science toy they'll keep coming back to.

What Is Colour Mixing and Why Should Kids Learn It?

Colour is everywhere — in the clothes we wear, the food we eat, the screens we look at, and the paintings we make. But have you ever wondered why mixing red and blue makes purple? Or why yellow and blue combine to create green?

Understanding colour mixing is one of the earliest intersections of art and science. When children learn how primary colours combine to form secondary colours, they are not just learning about crayons — they are building an intuition for light, physics, and creative thinking that will serve them throughout their lives.

At My Stem Lab, we believe the best way for children to understand science is to experience it firsthand. That's exactly what this activity does — it turns an abstract concept into something kids can touch, fold, and explore on their own.

What You'll Need to Build Your Pocket Colour Mixer

One of the best things about this project is that you don't need any expensive equipment. Here's everything required to make your DIY colour mixer:

Step-by-Step: How to Make Your DIY Colour Mixer (7 Easy Steps)

Ready? Let's build your pocket colour mixer! Follow these steps carefully, and don't rush — good results come from taking your time, especially with the cutting.

1. 1
   Cut the gelatine circles

   Using your divider or compass, draw three equal circles on your gelatine paper — one blue, one red, and one yellow. Cut them out carefully. They should be slightly smaller than the windows you'll cut in the next steps, so they fit neatly behind each opening.

2. 2
   Fold the card into three equal parts

   Take your postcard or thick cardstock and fold it into three equal sections, like a tri-fold brochure. These three panels will become the windows of your colour mixer. Make sure the folds are crisp and even.

3. 3
   Draw and cut three overlapping windows

   Using your compass, draw three equal-sized circles that slightly overlap each other in a row across all three panels. Then carefully cut out these three circular windows. This is the trickiest step — take your time and use sharp scissors. The overlaps are important!

4. 4
   Stick the gelatine circles behind the windows

   Open the card fully and stick each gelatine circle behind its corresponding window using a little glue around the edges. Place Blue in the middle window, Red on the left window, and Yellow on the right window. Use a small amount of glue neatly around the edges — too much glue can make the paper wrinkle.

5. 5
   Fold all layers together

   Fold the card back up so all three panels sit on top of each other. Test that the panels slide and fold smoothly over each other. If anything feels stuck, gently re-fold until movement is fluid.

6. 6
   Make a small pivot hole

   Using your needle, make a small hole near the bottom corner, passing through all layers of the folded card at once. This ensures all layers are aligned and the split pin will hold them all together properly.

7. 7
   Insert the split pin

   Push the split pin (press-button) through the hole and open out the two prongs at the back to secure it in place. This acts as a pivot, allowing the panels to swing open and closed freely. Your pocket colour mixer is now complete!

How to Use Your Colour Mixer: See Colour Magic in Action!

Now comes the best part. Here's how to use your new pocket colour mixer to discover the three key colour combinations:

1. View Each Colour Separately

Start by unfolding the card fully. Look through each window individually — you'll see a vivid red circle, a clear blue circle, and a bright yellow circle. These are your three primary colours in their pure form.

2. Mix Red and Blue → Purple!

Fold the Red window over the Blue window. Look at the overlapping area. What do you see? The red and blue combine to create a rich, deep purple. Try moving the panels back and forth to watch the purple appear and disappear — like magic!

3. Mix Yellow and Blue → Green!

Now fold the Yellow window over the Blue window. The overlap zone turns a vibrant green. This is one of the most satisfying moments in the activity — most children don't expect that yellow and blue can produce green!

4. Mix Red and Yellow → Orange!

Finally, try folding the Red window over the Yellow window to produce a warm, glowing orange.

The Science Behind It: What Is Subtractive Colour Mixing?

When white light (which contains all colours of the rainbow) shines through a red piece of gelatine paper, most wavelengths are absorbed except red — which passes through to your eye. When you add a blue layer on top, blue wavelengths pass through, and the overlap of what both layers allow through creates purple.

This is different from how light mixes on your phone or TV screen (called additive colour mixing), where combining Red, Green, and Blue light makes white. In subtractive mixing — which is how paints, inks, and dyes work — combining all three primary colours produces dark brown or black, because each layer keeps absorbing more light.

This is the same principle used in printing (CMYK ink), painting, and even how sunglasses filter light. With just a folded card and some gelatine paper, your child has just understood a concept that underpins photography, design, and colour theory!

Try This Next: Extend the Learning with More Colour Experiments

Once your child has mastered the basic colour mixer, here are some great ways to keep the curiosity going:

• Try other gelatine colours: What happens when you mix green and red? Or orange and blue? Challenge your child to predict the result before testing it.
• Make a colour wheel: Use the mixer results to draw and label a full colour wheel poster. Map out all primary, secondary, and even tertiary colours.
• Outdoor experiment — sunlight: Hold the gelatine paper circles up to sunlight and see how vivid the colours become. Compare natural light to artificial indoor light.
• Mix three colours at once: What colour do you get when you fold all three windows together? Discuss why the result looks dark or muddy — and connect it back to subtractive colour mixing.
• Try it with watercolour paints: Does the colour mixer's predictions match what happens when you mix the same watercolour paints? Compare and discuss any differences.

A Note on Safety

• Always use scissors carefully, and supervise young children during cutting steps.
• Do not point the needle towards yourself or others when making the pivot hole.
• Keep small items like the split pin away from very small children (under 3 years).

Frequently Asked Questions About Colour Mixing for Kids