the yellow? if you mean the background i believe thats part of the background picture
try and look for that in the client object browser
look for this
<widget class="inner_contrast_box" appearance="boxes/custom/interface/content/primary/paper">
<layout class="stick_to_object_attachment" id="align_top" get_side="top" set_side="top" target="mai1"/>
<layout class="stick_to_object_attachment" id="align_bottom" get_side="bottom" set_side="bottom" target="mai1"/>
<layout class="stick_to_object_attachment" id="align_right" get_side="right" use_recursive_search="true" set_side="left" target="side"/>
<layout class="stick_to_object_attachment" id="align_right" get_side="left" set_side="left" target="mai1"/>
<animation class="translate_animation" start_value="0, 0.2" end_value="0, 0" duration="0.4" end_mode="hold_end" tween="ease_out" coord_mode="relative_to_screen" />
<attachment class="test_multiple_globals_attachment" default_value="false">
<list id="get_properties">
<record get_property="MatS" test_mode="equal" value="true" skip_if_null="true" />
<!-- PROP_FULL_SCREEN_3D_BEING_DRAWN -->
<record get_property="Ma3D" test_mode="equal" value="true" comparison_mode="or" skip_if_null="true" />
<record get_property="HdBk" test_mode="equal" value="true" comparison_mode="or" skip_if_null="true" />
</list>
<integer id="set_property" value="hidn" />
</attachment>
</widget>
and then comment it out or delete the widget and see if thats what you're after
remember to always make a copy of the working file, so you always have a working backup if something goes wrong