“The power of the web is in its universality. Access by everyone regardless of disability is an essential aspect” (Tim Berners-Lee founder of World Wide Web (WWW) and W3C, 24 May 2006.)
This article will help you understand usability which is the ease of use and learnability of a human-made object.

The Web Accessibility Initiative (WAI) was set up by the W3C to promote accessibility on the Web. The WAI is attempting to educate people with disabilities on how to navigate on the Web and help developers.
There are numerous reasons why merchants should aim to improve the accessibility of their website or help disable people; first one concerns the law in many countries (for example in the UK and Europe since 2002); second one concerns social and economic reasons (important market).

According to INSEE (2001), there are 12 million disable persons in France (1.7 million have visual problems, colorblind) and 2.5 million among them navigates on website. That fact seems to be ridiculous since 8% of 35.3 million of internet users are disabled. This is important for e-marketing and our society in order to develop profits.

The characteristics of usable website and accessible for all

One of the core principles of the WAI is to make content on the web available to all regardless of any disability they may have, and propose alternative content.
A website should be perceptible and unrestricted access. According expert the website has to usable technical to make the navigation easier: 
– The color should be considering. A useful tool for designers can be found, which provides several different filters that mimic how different types of color-blind users would perceive a website (on colorfilter.wickline.org thank to the URL)
– Propose content can be perceived to different manner and the text have to have a good contrast and should be resizable (fluid design), in order to facilitate the navigation.
The level of contrast between foreground and background is important of the website. A high level of contrast will benefit everyone.  Of course the safest option is always black text on a white background or vice versa (Color Contrast Analyser).
 Monochrome can also use which offers color blind visitors a way of easily appreciating your design, even if they can’t necessarily identify the intended colors.
– The website should including a transcript of the conversation for users to download or read on the site: for example add captioning to the video thank to using speech recognition software, for the visually handicapped (test by youtube: http://captiontube.appspot.com/), these element favored the comprehension in a website.
– The website must propose a navigation shortcuts to help a keyboard user navigate to certain sections of a website quickly

Example: Website method especially for color-blind person

The colorblind have experience affected a decreased ability to distinguish colors from others.
However, more common cases are an inability to recognize blue/yellow or red/green.

Hue, Saturation & Brightness
Modifying the hue, saturation and brightness of colors can help us show definition and allow users to distinguish, without using multiple colors.

Selecting colors with specialist Tools
There are a couple of online tools that will allow you to simulate individual colors under color-blind circumstances; these tools offer some insight into what color-blind visitors will see.

Bibliography:

–    Shaun Cronin (2011), 6 Tips for Improving Website Accessibility, http://webdesign.tutsplus.com/articles/general/6-tips-for-improving-website-accessibility/?search_index=2

–    Connor Turnbull (2011), Designing For, and As, a Color-Blind Person, http://webdesign.tutsplus.com/articles/design-theory/designing-for-and-as-a-color-blind-person/?search_index=1