It’s very important for a designer to test images or website design against color blind vision for accessibility purpose. According to W3C accessibility standards a website’s text and graphics should be understandable even without colors.
Roughly 1 in 20 people have some sort of color vision deficiency. -Vischeck
A website should be designed keeping this in mind so that it be accessible to the people who are suffering from color blindness and therefore it could reach a wider audience.
Vischeck offers free online and offline tools to check website or images for color blind vision. It allows you to check against three type of color deficient visions – Deuteranope, Protanope, Tritanope.
You can also download Vischeck Photoshop plugin
Also checkout the following two magnificent articles by HellBoundBloggers intended to help Visually Impaired Users: