HSVGradient.qml

import QtQuick 2.5
import QtGraphicalEffects 1.0

Item {
    LinearGradient {
        anchors.fill: parent

        y: parent.height / 2

        start: Qt.point(0, parent.height / 2);
        end: Qt.point(parent.width, parent.height / 2);

        cached: true

        gradient: Gradient {
            GradientStop {position: 0/6; color: Qt.rgba(1, 0, 0, 1)}
            GradientStop {position: 1/6; color: Qt.rgba(1, 1, 0, 1)}
            GradientStop {position: 2/6; color: Qt.rgba(0, 1, 0, 1)}
            GradientStop {position: 3/6; color: Qt.rgba(0, 1, 1, 1)}
            GradientStop {position: 4/6; color: Qt.rgba(0, 0, 1, 1)}
            GradientStop {position: 5/6; color: Qt.rgba(1, 0, 1, 1)}
            GradientStop {position: 6/6; color: Qt.rgba(1, 0, 0, 1)}
        }
    }

    Rectangle {
        anchors.fill: parent
        color: "transparent"
        border.color: "black"
    }
}