Use subtler grey for emulated toolbar toggle on OS X

Use a lighter shade of gray to avoid problems with user icons and to
match the look of OS X 10.10's rendering of selected toolbar items.

Fixes #16645.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@78075 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775