It's a bit hard to suggest starting places without knowing how the css relates to the HTML, but have you analysed the code using something like firebug? Here's a couple of questions I'd ask when looking at the css:
2. Where else does the colour #ffc426 appear in the css? That will help identify what rules sets might be setting the colour.
3. If commenting out that line sets a background-color:black, it must be inherited from somewhere - where is black specified as a background-color? That might be a clue as to what style rule is over-riding the black and setting gold.
4. Given this only happens on mouse click, is there a colour set for :active in the css?