QGraphicsTextItem :: paint()的默认实现与 QStyleOptionGraphicsItem :: palette 无关..如果要使用其他颜色，则必须实施自定义绘画.

The default implementation of QGraphicsTextItem::paint() doesn't care about QStyleOptionGraphicsItem::palette. You have to implement a custom painting if you want different color.

这是简化的方式:

class CMyTextItem : public QGraphicsTextItem
{
  public:
    virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) override
    {      
      QAbstractTextDocumentLayout::PaintContext ctx;
      if (option->state & QStyle::State_HasFocus)
        ctx.cursorPosition = textCursor().position();

      if (textCursor().hasSelection()) 
      {
        QAbstractTextDocumentLayout::Selection selection;
        selection.cursor = textCursor();

        // Set the color.
        QPalette::ColorGroup cg = option->state & QStyle::State_HasFocus ? QPalette::Active : QPalette::Inactive;
        selection.format.setBackground(option->state & QStyle::State_HasFocus ? Qt::cyan : ctx.palette.brush(cg, QPalette::Highlight));
        selection.format.setForeground(option->state & QStyle::State_HasFocus ? Qt::blue : ctx.palette.brush(cg, QPalette::HighlightedText));

        ctx.selections.append(selection);       
      }      

      ctx.clip = option->exposedRect;
      document()->documentLayout()->draw(painter, ctx);

      if (option->state & (QStyle::State_Selected | QStyle::State_HasFocus))
        highlightSelected(this, painter, option);
    }
};

但是，此解决方案并不完美.不闪烁文本光标是一种缺陷.可能还有其他人.但是我相信稍微改善一下对您来说并不是什么大问题.

However, this solution is not perfect. Not-blinking text cursor is one imperfection. There are probably others. But I believe that improving it a little will be not that big deal for you.