Ten years ago, Greg Tang was looking for a better way to teach math to his kids. He wound up creating a groundbreaking series of picture books that included the New York Times best seller The Grapes of Math. His books quickly became staples in school libraries and university teacher training programs, garnering numerous awards and selling over a million copies. The free online version of The Grapes of Math.
The Grapes of Math is indeed a lovely book, and immediately raises a very interesting question: it uses colour coding of information, which appears to be forbidden in the institutional use in this country by law (adopted from the EU legislation), and, I have to agree, for good reason: 1 person in 20 is colour blind or have significant deficiency of discrimination of colours. American homeschoolers, if their children are not colour blind, can of course ignore this issue and use colour coding, a powerful didactic tool. But I, as a lecturer to a class of 280 students, cannot ignore the issues of equality of access: 1 in 20 for me means 14 students, I cannot damage their chances to learn.
By the way, the Wiki article on colour blindness contain some tantalising snippets:
About 8 percent of males, but only 0.5 percent of females, are color blind in some way or another, whether it is one color, a color combination, or another mutation. [...]
Any recessive genetic characteristic that persists at a level as high as 5% is generally regarded as possibly having some advantage over the long term, such as better discrimination of color camouflaged objects especially in low-light conditions. At one time the U.S. Army found that color blind people could spot “camouflage” colors that fooled those with normal color vision.[not in citation given]