Understanding WCAG 2.0 - criteria 1.4.8

I'm having trouble understanding the WCAG 2.0 criteria 1.4.8.

From what I understand it basically says that if I have for example a <div> that I define both background and text color in, I will have to either:

Provide a color picker tool for that div so that the user can change those colors
"G156: Using a technology that has commonly-available user agents that can change the foreground and background of blocks of text"

Providing a color picker sounds pretty far fetched, so I'm placing my hopes on "G156". Does a regular web browser (ie,firefox,opera etc.) qualify as such an user agent?

Another confusing part is the "common failure" where it says "F24: Failure of Success Criterion 1.4.3, 1.4.6 and 1.4.8 due to specifying foreground colors without specifying background colors or vice versa", which I sort of interpret as "as long as you specify both background and text color for that div, your safe".

Any thoughts on how to interpret this WCAG criteria?

Solution

Does a regular web browser (ie,firefox,opera etc.) qualify as such an user agent?

According to http://www.w3.org/TR/2010/NOTE-WCAG20-TECHS-20101014/G156, it seems so. It says:

Tests

Procedure

Open the Web page in a browser that allows users to change colors of HTML content.

Change the foreground and background colors in the browser settings so they are different than those specified in the content.

Return to the page and check that that the new specified foreground text and background colors in the browser override the colors specified in the content.

Expected Results

Check #3 is true.

"as long as you specify both background and text color for that div, you're safe"

I think so. It means don't just assume the background is white, because if you don't explicitly specify it, it might not be.