Red and green. It’s hard to imagine two more different colors (in fact, they’re complementary, or opposites, on the color wheel). But to people with the most common type of color-blindness, they can be indistinguishable.

That’s why Mattel’s Uno is getting a makeover. The card game, which is played by matching colors and numbers, today debuted a new version that’s friendly to people with all types of color-blindness, thanks to a bit of iconography provided by the ColorADD standard–an accessibility system for color-blind people. Now, a small icon next to the numbers on Uno cards will define its color.

For most toys, such an announcement would be small news. But Uno is the most popular non-collectible card game in the world, and the fourth most popular toy across the entire industry. That success is largely due to Uno’s inclusive design. Much like a typical deck of cards, it’s playable by anyone.

“It’s language agnostic–colors and numbers. You can play that with almost any two people around the world,” says Ray Alder, Senior Director, Global Games at Mattel. To Mattel, universal accessibility is the very core of Uno’s brand, but its red, green, yellow, and blue language had a major oversight. “Someone [internally] said, ‘Actually, it’s not totally inclusive. What if you’re color-blind.”

This led Mattel on a 60-day redesign of Uno. The company considered changing its well-known color scheme, to avoid that red and green mix up, but ultimately, it realized “red and green [color-blindness] are what most people have, but there are all different types,” says Alder, alluding to problems some people have seeing colors like yellow and purple, too. “We couldn’t just change a red card to another card or green card to another card, because some people still couldn’t tell the difference.”

Ultimately, Mattel adopted the burgeoning ColorADD standard, a design system which uses iconography to identify colors. It’s a somewhat ingenious bit of graphic design work if you’ve never seen it. The basic colors red, blue, and yellow each get their own shapes. Then by combining these shapes–say, the slash of yellow and the triangle of blue–you get new colors, like green. Not only does ColorADD label colors, it visually explains the additive mixes that create those colors, too.

The changes to the game are minimal: Uno places ColorADD icons next to each number, and places them on each color of the wild card, too. Otherwise, the game is unchanged. Casual players might not even notice a difference.