Lubuntu 17.04 LightDM Greeter panel font hard to read

The Host-Name and the clock in the Lubuntu 17.04 LightDM Greeter panel are either the same color as the background, or are almost so - it is impossible to read them, but it is - barely - possible to tell that they ARE there.

I have looked in the Properties->Installed Files for the package, and discovered the file:
/etc/lightdm/lightdm-gtk-greeter.conf (and then found the apparently (originally) identical /etc/lightdm/lightdm-gtk-greeter.conf.d/30_lubuntu.conf file in my File Manager - Nemo.

The only Panel options (changeable with "sudo lightdm-gtk-greeter-settings") are "panel-position", "clock-format", and "indicators", so I assume that the font-related aspects are derived from Appearance: theme-name.

This defaults to "Lubuntu-default".

The only other option is "Lubuntu-dark-panel". This sounds promising, and I have now set it to that, but have not yet logged out or in to see if that solves the problem.

I will report back to say if it is now fixed or not.

As defaulted, it is impossible to read.

I note that the Panel Font is Ubuntu Regular - 0. I assume the 0 means "get actual font height from somewhere else"

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scott@scott-ASUS-M2N68-AMPLUS:~$ uname -a
Linux scott-ASUS-M2N68-AMPLUS 4.10.0-20-generic #22-Ubuntu SMP Thu Apr 20 09:22:42 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
scott@scott-ASUS-M2N68-AMPLUS:~$ lsb_release -dsc
Ubuntu 17.04
zesty
scott@scott-ASUS-M2N68-AMPLUS:~$ echo $DESKTOP_SESSION
Lubuntu

lightdm-gtk-greeter 2.0.1-2ubuntu4
lightdm 1.22.0-0ubuntu2
lightdm-gtk-greeter-settings 1.2.1-2
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ProblemType: Bug
DistroRelease: Ubuntu 17.04
Package: lightdm-gtk-greeter 2.0.1-2ubuntu4
ProcVersionSignature: Ubuntu 4.10.0-20.22-generic 4.10.8
Uname: Linux 4.10.0-20-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.20.4-0ubuntu4
Architecture: amd64
CurrentDesktop: LXDE
Date: Mon May 8 17:41:41 2017
InstallationDate: Installed on 2017-04-22 (16 days ago)
InstallationMedia: Lubuntu 17.04 "Zesty Zapus" - Release amd64 (20170412)
SourcePackage: lightdm-gtk-greeter
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.lightdm.lightdm-gtk-greeter.conf: [modified]
mtime.conffile..etc.lightdm.lightdm-gtk-greeter.conf: 2017-05-08T17:12:00.600729