MATE 1.20 and Current
 

In the Control Center -> Apearance -> Themes, Customize dialog, I no longer see a Colors tab. Is this correct or am I missing some kind of dependency?

Thanks. :)

Yes, it has been removed.
Detailed explanation is in this issue

The GTK3 devs strike again -- the usual fuster cluck.

Of course, not your fault Willy. :)

Are there any work-arounds?

For example, I like to use a pink background (#FDD9E6) as a reminder in apps that I open as root user. Some apps provide a built-in reminder, such as Thunar, but for me the colored background is more obvious.

Well, since it's not supported by the toolkit itself, there's nothing the developers can do about it.

Well, since it's not supported by the toolkit itself, there's nothing the MATE developers can do about it. The GTK3 devs are a different story. :)

Sorry for the snarky thread. Just an example why sometimes users get cycnical about free/libre software. You get what you paid for -- "ain't broke then reinvent the wheel until broken" seems to the motto of the GTK3 devs. Of course, "GTK3 devs" is a nice way of saying GNOME devs. :(

Thanks to you and Chess for your efforts. :)

Chess Griffin is no longer maintaining MATE SlackBuilds, so it's just me now

Thanks nonetheless to both of you. :)

Isn't also that the reason for why Darth Vader gone on rants about Plasma5, so many times? Apparently, this behavior is not specific only to the GNOME devs.

Except KDE developers aren't QT developers. They just use the QT toolkit and can only use what the QT devs put out. When the QT devs EOL QT4 for QT5, KDE developers either stick with an older unsupported version or they migrate to the newer version.

GNOME and GTK are both done by the GNU project.

In fact GTK is a spinoff of the gimp project, the name used to stand for
Gimp ToolKit
Of course gimp and gnome are some of the many projects under the GNU umbrella.

I actually didn't know that. Wikipedia has more info on that:

BTW: the GDK library is gimp-derived too, the abbreviation stands for Gimp Drawing Kit.
See this wikipedia page
en.wikipedia.org/wiki/GDK
So both these libraries are not directly related to the gnome project (although gnome does make use of them, of course).

Except that they are mainly developed by the GNOME Project.

Gnome hijacked Gtk for their own ends, and trampled all over the wishes of other teams dependent on Gtk - Xfce and Lxde, for example. If Gtk is mainly developed by the Gnome team today it's because everyone else gave up on it. Xfce, unfortunately, are too deeply committed at this stage to Gtk, and have to submit to the Gnome diktats or die.

This is a ridiculous rant. The GTK toolkit is very good, as I can see it used in MATÉ. Qt can provide more bells and whistle but is way behind GTK in some fields, like one which matters to me: accessibility to the blind users. As a result accessibility of MATÉ is second to none among Linux desktops.

As an aside, strip from your Slackware all software developed under the Gnome umbrella (list here) and see what happens ;)

Also, not all the software they host are managed by them: for instance the Orca screen reader is developed by Joanmarie Diggs from Igalia and I can tell you with certainty that she is the only person who makes decision for Orca.