lxappearance doesn't offer the ability to change the gtk colors without
lxsession anymore.

Setting the gtk-color-scheme property in the gtkrc 2/3 files however doesn't
really require lxsession in any way.

Yes, it is unavailable now to reflect the fact it requires XSettings daemon
to work. Yes, you can set gtk-color-scheme property in ~/.gtkrc-2.0 file
but unfortunately it will never affect colors of theme unless a XSettings
daemon is running (and then lxsession provides such service), that happens
just because each and every theme resets color when is loaded and only way
to change them after that point is a XSettings daemon. And there were few
bugreports about this before. Feel free to experiment with it to ensure
yourself. I'm sorry to disappoint you.

lxsession, but only for a valid _XSETTINGS_S* atom.

There are several alternative XSETTINGS daemons: xsettings-kde and
xsettingsd come to my mind, but probably gnome-settings-daemon would
also work.

Yuri D'Elia has written on Monday, 20 October, at 18:25:

You are right about that and upstream is aware of that, just needed a
reliable way to detect XSETTINGS daemon presence, and also mechanism to
store color value in that XSETTINGS daemon data. If you can provide a
well tested patch within next few days then that would be awesome and
updated lxappearance would appear in Debian unstable repository later
this week. Otherwise that will be possible only after Jessie release due
to scheduled freeze period.

Thank you very much.

I won't definitely have time to provide a patch for this, sorry.

Yuri D'Elia has written on Monday, 20 October, at 19:34:

You have nothing to be sorry for. Don't worry, upstream eventually add
support for other XSETTINGS daemons, just not right away. Thank you very
much for the notice. We will update Debian with this as soon as it is
available.