Some questions have a yellow background to them, what is the meaning of this?
The background color that you see is to show that the question contains a tag that you have selected as a "watched tag". Based on the tags on the questions that are highlighted in your screenshot, it appears that the watched tag in question is story-identification.
You can set which tags you are watching in the box at the upper right hand portion of the homepage:
If you click on the "Watch a tag" button in that box it will give you a space to type in tag names:
As you start typing it will give you suggestions of tags to select:
Simply find the tag you want and click the add button.
Now the tag will appear in the "Watched Tags" box:
If you want to remove a watched tag, simply click the "edit" button that now appears in the box. This will create an "x" on the tag icon:
Simply click the "x" and watch the tag disappear:
You are now back to the beginning.
Note that if you never clicked out of the "Watched Tags" box after adding the tag, you won't need to click the "edit" button in order to be able to remove the tag. You will already be presented with the tag icon having the "x" on it, so you can remove it right away.