Does Your UX Suck? Principle #2: Legibility of Text for All your visitors

Colour of Text
“Dark-gray on light-gray may seem stylish” says Dr. Peter J. Meyers1 , but due to browsers rendering colour unreliably, websites with poor contrast between text and background may be risky for legibility of your site. Dr. Meyers also suggests that font sizes should err on the side of too big and the recommended starting point is 16pts.
You know at least 1 in 10 men are colour blind and poor contrast is an issue for sufferers of colour blindness, so your choice for text colour and backgrounds needs to be made carefully. For visitors to your site, clicking on buttons you can't read can be a frightening experience.

Access
Be aware that sight-impaired visitors use ALT tags to read your site, it's an industry standard and law that sites be accessible to vision impaired folk, so Alt tags need to be included on your site. An Alt tag is visible to sighted readers, you've all seen a yellow tool tip like label appear with the name of the image when you place you cursor over the image on your site. Vision Impaired can set their computer to speak the Alt tag label.
 Insist your designers follow standard and insist on Alt tags.

Standards
More interestingly though, missing Alt tags indicate that your site probably isn't being "validated", either. Validation is a process used to eradicate errors in the code of your site. When you test a website for validation, you eradicate known issues that cause browsers to mess up your site. If your site was "validated" before release, missing Alt tags would set off alerts throughout, and many other more important errors would be highlighted and fixed before release. Expect that your site should be Validated and a company who doesn't care about Validation isn't providing you with a professional product.

1. Dr. Meyers, P.J. 2012. Usereffect, Strategic
Web Usability: 25-point Website Usability Checklist.
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