Why is color contrast important in software design?

Designers and product managers often ask me why color contrast and the ability to zoom in is important in software design. There are two groups of people who benefit from color contrast.

1. Color blindness. 1 in 12 men are color blind. 1 in 200 women are color blind. Any design that adjoins two different colors with the same or similar value can be tricky for color blind users to navigate. Additionally, the use of color only as an indicator of system status becomes meaningless. For example, red for alert and green for ok. If those two colors appear the same to a user, the meaning is lost. Therefore, any time a design uses color for meaning, it should be accompanied by a symbol or text that also provides meaning. A red exclamation for alert and a green checkmark for ok will provide a way to convey meaning without color alone.

2. Low vision. Around 3-3.5% of the world population has low vision.  Low vision users can be aided by increased color contrast in addition to the ability to zoom in or magnify their view of software on a screen. Zooming and contrast can be enhanced by peripheral hardware and software, but at a minimum, software should have a certain amount of contrast built in as well as the ability to adjust the zoom.

Further reading:
http://designshack.net/articles/accessibility/design-for-everyone-considering-accessibility-in-visual-projects