Human-Computer Interaction 3e Dix, Finlay, Abowd, Beale
When Gmail detects that a mail may be spam or phishing, it sometimes shows the following banner at the top of the mail:
I guess it could have been worse and used green text on a red background, but honestly!
The sad thing is that this is an important message (hence the red box to catch attention), but the amateurish appearance makes it seem more likely to be part of the spam mail itself (see the dynamics of trust). Indeed I checked the mail message source to make sure it was not a phishing attack!
Technically, this is an issue of contrast, our eyes are far better at light/dark distinctions than distinctions in hue. While the blue text is a very different colour from the red background, it is not very different in terns of level of arknss. In Chapter 5 of the HCI textbook we suggest viewing images or web pages in pure grey scale as a quick and dirty check for readability. Here is the greyscale version of the image– it is hard to read the links in either the orginal or this.
This is hard enough for fully sighted readers, but totally unreadable for those with any form of impairment or in poor lighting conditions.
Happily, it is probably no worse (but no better) for those with colour blindness. Here is a simulated image by vischeck.com: showing what the message might look like for someone with Deuteranope (the most common forms of red/green colour blindness):
(This case study first appeared as a blog entry "getting colours wrong" on HCIcourse.com.)
Alan Dix, 2012