How to deal with satellite image: rgb,nir,red, blue

I have purchased an image from GeoEye. The delivered files contain 4 files of equal size .tiff files. the names are blu,grn,nir,red. If i open them in ERDAS image viewer they appears in black and white. can I merge them some how and visualize them in real color or something. Can any one help me?
Comments
Let me know if I can be of further assistance.
Thanks,
Mike
Global Mapper Support
support@globalmapper.com