just overide the data function in your model, it looks like this
Qt Code: 
  1. QVariant MyTestModel::data(const QModelIndex &index, int role) const
  2. {
  3.     switch(role)
  4.     {
  5.     case Qt::DisplayRole:
  6.         return QVariant(QString(tr("%1")).arg((index.column() + 1) * 1000 + index.row() + 1));
  7.     case Qt::BackgroundRole:
  8.         switch(index.column() % 3)
  9.         {
  10.         case 0:
  11.             return QVariant(QColor(Qt::red));
  12.         case 1:
  13.             return QVariant(QColor(Qt::green));
  14.         case 2:
  15.             return QVariant(QColor(Qt::blue));
  16.         default://only to disable warning
  17.             return QVariant(QColor(Qt::white));
  18.         }
  19.  
  20.         break;
  21.     default:
  22.         return QVariant();
  23.     }
  24. }
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the BackgroundRole for the item's background color
the ForegroundRole for the text color