Instructions
Drag and drop the .MESH file into OgreXmlConverter.exe, which should be found in the OgreSDK/bin.
Open the resulting XML file in your preferred 3-D editor program, such as 3ds Max, Blender 3D or FreeWorld3D.
Look for the line that says "setAmbient(0, 0, 255);" and change the numbers. They are the red, green and blue values. You can set them between 0 and 255 for different shades.
Reapply the changes to your mesh.