- How different colors encourage or discourage people from buying, or even from sticking around for a second click.
- How images (of people, of products, of pets) affect whether people will buy, register for my site, click on a link.
- How design affects download time for webpages, and how download time affects people's willingness to stay on a site.
- How a/b or multi-factorial testing works, and why that matters for a designer.
- How to balance the SEO value of actual text, vs the "it looks pretty" value of images of text.
Anyway, end of rant. But here's a useful article that talks about some of the implicit meanings of color.