IBus pre-edit segment color is not drawn

The desktop environment is Plasma X11 and using QT_IM_MODULE=ibus environment variable.

To reproduce:
1. Run kwrite with QT_IM_MODULE=ibus
2. Enable ibus-anthy and Hiragana mode
3. Type "watashinamaehapendesu." keys and space key
4. The whole the string is drawn with a black underline but the activated segment color is not drawn.

qtbase/rc/plugins/platforminputcontexts/ibus/qibusplatforminputcontext.cpp:QIBusPlatformInputContext::updatePreeditText() sends the pre-edit segment color against whole the pre-edit string using QinputMethodEvent but the color is not drawn in kwrite and konsole.

I know Wayland input-method protocol does not support the preedit colors yet but the colors had worked in Plasma X11. Maybe after Plasma Wayland was integrated, the regression was also integrated in Plasma X11.