The white balance tables for the Nikon D3100 in Lightroom 4 are faulty. They have been fixed in Lightroom 5.4+. This means if you upgrade Lightroom 4 to Lightroom 5.4+, your white balance will be wrong for all your finished Raws that use non Adobe Standard profile/s (i.e use camera Standard/Neutral, Porttait etc)
More info:
Lightroom: 5.4 broken with D3100
More info:
Lightroom: 5.4 broken with D3100