I'm currently working on a Stryker, i'v came across a problem which make it so one of the faces reflects light differently than all of the others.
This is a problem related to the normals. To correct it, go into edit mode and select everything. (This can be done by pressing A once or twice.) Then, click Shading/UVs > Normals > Recalculate. If this does not work, select the single face and click Shading/UVs > Normals > Flip Direction.
If you open up your preference and look under the System Tab you will see Solid OpenGL lights. They are the defaults to help you see 3D surfaces that face different directions - it is just an aid and does not affect the render. If a face goes severely dark then the chances are the Normal's are flipped. In your case nothing to worry about...
If you want to check your Normals though, there is always the button under Mesh Display.