GRASS GIS like other GIS imaging processing software splits a multiband raster into individual bands on import. This is to allow preparing various analysis results from individual band combinations, such as false color images or NDVI from satellite data. For example Landsat 8 contains 11 bands. Bands 5 and 4 can be used to calculate NDVI. Bands 5,3,2 are sometimes used to produce false color images.
If you need to recombine the imported bands for visualization, the
r.composite module does this. You can create a true color composite by passing the
b parameters the bands that should appear as red, green and blue. i.e. (the Landsat 8 example)
r.composite r=band.4 g=band.3 b=band.2 out=l8_rgb_composite