Ubuntu – How to create in QML a table of TextInput boxes with background

This is not an answer to your question since the dialog text is not directly changed, but it might be an answer to your problem, since the dialog text changes itself dynamically :-)

Assuming that you have some item that triggeres the onSomethingHappened, you could connect properties of the dialog to properties of the item.

Example:

Item {
  Component {
     id: dialog
     Dialog {
        id: dialogue
        title: someID.dialogTitle
        text: someID.dialogText
        Button {
            text: "cancel"
            onClicked: PopupUtils.close(dialogue)
        }
     }
  }
}

SomeItem {
  id: someID
  property string dialogTitle
  property string dialogText
  onSomethingHappened: {
     dialogTitle = "Hello David"
     dialogText = "Whats up?"
     PopupUtils.open(dialog)
  }
}

The Ubuntu SDK comes with its own styled TextField element. On dark background you can use the default Qt version by importing QtQuick.Controls (14.04 only). It will always render a white background but can also be styled with TextFieldStyle:

import QtQuick 2.0
import Ubuntu.Components 0.1
import QtQuick.Controls 1.1
import QtQuick.Controls.Styles 1.1

MainView {
    width: 400
    height: 300
    backgroundColor: "black"

    Column {
        spacing: units.gu(2)
        anchors.centerIn: parent
        TextField {
            placeholderText: "ask"
        }
        TextField {
            placeholderText: "Enter text"
            text: "ubuntu"
            style: TextFieldStyle {
                textColor: "black"
                background: Rectangle {
                    radius: 5
                    color: "gold"
                    implicitWidth: 100
                    implicitHeight: 24
                    border.color: "#333"
                    border.width: 1
                }
            }
        }
    }
}

It will look like the screenshot below:

Source: http://qt-project.org/doc/qt-5/qml-qtquick-controls-styles-textfieldstyle.html