An example of the problem coloring a header...

headerHack.qml

import QtQuick 2.0
import Ubuntu.Components 0.1
import Ubuntu.Components.ListItems 0.1 as ListItem

MainView {
    id: mainView

    width: units.gu(40)
    height: units.gu(60)

    Rectangle {
        id: headerBackground
        height: header.height
        width: header.width
        anchors.fill: header
        color: "#288369"
    }

    Tabs {
        id: tabs

        Tab {
            title: i18n.tr("Pretty Hack")
            page: Page {
                Label {
                    anchors.centerIn: parent
                    text: "Sure looks nice here,\nbut check out the other tab."
                }
            }
        }
        Tab {
            title: i18n.tr("Ugly Hack")
            page: Page {
                ListView {
                    id: list
                    spacing: units.gu(1)
                    anchors.fill: parent
                    model: model
                    delegate: ListItem.Standard {
                        text: model.info
                    }
                }

                ListModel {
                    id: model

                    ListElement {
                        info: "First item"
                    }
                    ListElement {
                        info: "Second item"
                    }
                    ListElement {
                        info: "Third item"
                    }
                    ListElement {
                        info: "Fourth item"
                    }
                    ListElement {
                        info: "Fifth item"
                    }
                    ListElement {
                        info: "Sixth item"
                    }
                    ListElement {
                        info: "Seventh item"
                    }
                    ListElement {
                        info: "Eight item"
                    }
                    ListElement {
                        info: "Nineth item"
                    }
                }
            }
        }

        Component.onCompleted: {
            tabBar.__styleInstance.headerTextSelectedColor = "white";
        }
    }
}