First of all, you can get the raw materials at
Michael's or any other art store.  At the framing
counter, you can buy the uv glass, mat board and
foam board.  Near there, they usually have frames
and pre-cut mats.  Also, pick up acid-free tape.

If you buy by the sheet and cut yourself, you can
frame a standard-sized cel for about $40.  I have
several of these that I change cels in every few
months to change my decorations.

Here is a real good guide to framing:
http://users.animanga.com/kallred/FrameIt.html
One point that he makes that I'd like to stress
since I've gotten bit by it before is to make
sure that your frame is deep enough to hold the
entire package.

As far as colors, the recommendation that I have
is more of a 'what not to do' and that is not to
choose the major color of your character to be
the mat color.  Instead, choose a color that
contrasts the major color or that matches a minor
color in the cel.  This makes the cel stand out
from the mat rather than blend it to it.  In your
case, a brown mat would be a really bad choice as
her eyes and hair would blend in with it.  I've
got a similar cel of Jubei that I've done with a 
dark green and thought it worked out well.  If
you've got photoshop, etc...edit your scan and
play with color schemes and see what you may
like.

Hope this helps.