Fix compilation on Yocto

Summary:
By default, Qt is built without accessibility there, which is what
would indirectly include the needed QColor with a "normal" Qt build
here.

Reviewers: #frameworks, broulik

Reviewed By: broulik

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D7117

src/declarativeimports/core/colorscope.cpp

@@ -23,6 +23,7 @@
 
 #include <QQmlContext>
 #include <QQmlEngine>
+#include <QColor>
 
 QHash<QObject *, ColorScope *> ColorScope::s_attachedScopes = QHash<QObject *, ColorScope *>();