on understanding rgb color

May 29, 2009

Last week I wanted to teach the kids how to create a randomly colored shape, which (in Shoes) would use a fill color like this:

fill rgb(0..255.rand, 0..255.rand, 0..255.rand)

I figured they could easily grasp the random number syntax, but creating colors as a mix of red, green, and blue? They are used to primary colors of red, yellow and blue. It is totally weird that green and red make yellow, and downright amazing that red, green and blue make white. You have to be an old school graphics geek like me or someone who does stage lighting to have gained any intuition about how these kinds of colors mix. Most folks, elementary school students included, only have experience mixing colors with paint or dye, where red and green make brown. That is called “subtractive” color mixing. When we mix light (and pixel values), it is called additive color mixing.

To explain this, I put together a neat physical demonstration with the help of my friends, Paul & Glen, from Emotion Studios, and Janet from JCX Expendibles. (As a side note, I must say that if you live in San Francisco, enjoy this article and periodically need random materials for your crazy projects you must visit JCX on Harrison Street. It is awesome.)

My goal was to create three spots of color (red, green, and blue), then mix them to create white where they overlap. This looks much cooler in real life…

I ended up finding it could work using three Mini Maglight flashlights (about $14 each, which adds up but I figured I could use them for camping later). The front of each light is covered by a gel. I used the following colors from Lee Filters (the big sheets are $6 each, but I bet if you called them up they would send you a sampler). I used these colors:

I highly recommend this demonstration when teaching anyone about rgb color. This would even make a fun early physics experiment for first graders.