I'm not sure this is something you'll be able to test with just JavaScript. You might be able to do something with Selenium/WebDriver, but even then checking for the current background color in a test like that seems like more effort than the test is really worth. The problem is that this interaction is handled entirely by the browser without any JavaScript code at all. You would have to actually move the mouse over the element with the `:hover` pseudo-selector attached in order to get the browser to make the change.
Hope this helps. Thanks for using Jasmine!
-Gregg