The festive Christmas color combination of red and green has high contrast for most people. For a mostly male minority (7 to 10%) with red-green color blindness there instead is little or no contrast. To them that color pair just is an effective form of camouflage. When you choose colors for graphics you should consider that accessibility problem.
A few days ago I saw a blog post about PowerPoint Slides for Color Blind Audiences. It discussed using an online tool called Vischeck that lets you upload and then see an image (.png or .jpeg file) the way someone with color blindness would. There are three options in the online tool: deuteranope, protanope, and tritanope. The first two types are red-green color blindness.
Try Vischeck on this cute clipart image of Santa Claus with a set of drums. For a deuteranope his bright red suit and green drums both will be perceived as being olive drab, so Santa will just have joined the army.
In a previous post on this blog (September 16, 2008) I referred to an article by Professor Stephen Few on Practical rules for using color in charts. The red and green in his palette of soft natural colors shown near the bottom of page 6 are almost indistinguishable if you have a color blindness problem.
I also thumbed through my copy of Garr Reynold’s otherwise wonderful book, Presentation Zen, and found examples of Christmas red-green combinations on pages 137, 168, and 169.
Back on February 1 on his Slides that Stick blog Jan Schultink discussed “Using historical paintings as an inspiration for color schemes”. He showed a palette of five colors borrowed from a Van Gogh painting, "Night Cafe Arles". I commented on it, and on February 10 he posted again on “PowerPoint template colors and color blindness.” The original palette is shown at the left, and what a deuteranope would see is shown at the right. The Van Gogh green and red are easily distinguishable, but surprisingly the brown and brick red are not.
How do you tell if an Irish-American man is color blind? It’s easy. He’s the only guy in the crowd dressed up for St. Patrick’s Day in Christmas colors of red and green.