Is it a faux pas to ask for a colleague's figure in a separate but related publication? I'm an undergraduate with virtually no experience with the expectations of academia (so I apologize in advance for the silly question). I'm finishing up a paper describing my research and would like to include a figure to describe something in my "Background" section. 

There is a graduate student in my lab who has a paper dealing with the background topic and has a perfect image that I'd like to use as said figure. The paper has been accepted but not yet published. Would I be violating some protocol if I asked to use the identical figure? If not, what is the proper way to attribute the figure to the original source? In the caption?
You can always ask, then it is the choice of the author to accept or not. As for the citation, if the paper is accepted but not published, you can have a note in the citation &quot;to appear&quot;. For instance, your text could like:

Following [Alice12], we describe ... as illustrated in Fig.1.
[Alice12] Alice, paper, journal, accepted, to appear.