e.g. without hidpi this could probably be reproduced with
export SAL_USE_VCLPLUGIN=gtk3
export GDK_BACKEND=x11
export GDK_SCALE=2
and CppunitTest_cppcanvas_emfplus fails with 0x00ff00 instead of 0x00fe00

Change-Id: I1ecd7dce7703ed50fe396e007424a3ec4252d063