@sgunhouse Thanks! I did not know where to find those controls. It helps to have directions.

@sgunhouse Yes! In Opera 12.16, I entered opera:config as the URL. I changed the setting for Dialog Toolkit from 0 to 4. I restarted Opera. My menus are now in black text. Hooray! Some of the bars and backgrounds have turned light purple, but that's tolerable. Thank you for helping me!

@sgunhouse I'm working with an older machine (AMD Athlon XP 1800+ 1.53 GHz, 640M RAM, (originally ran XP) now running Xubuntu 16.04.3 LTS 32-bit. I've got a topic open at https://forums.opera.com/topic/23262/xubuntu-16-opera-12-16-browser-menu-stubborn-light-green-text-problem-how-change , and you just posted a good lead there for me. My plan for the next thing to try is to remove Opera and Firefox, install a desktop theme, re-install Opera 12.16, and report in with my results.

@nikt11 Thanks for your help so far! Here's my terminal text. I had to tell it where to find the file:
gary@Desktop1:~$ sudo dpkg -i opera-stable_45.0.2552.898_i386.deb
[sudo] password for gary:
dpkg: error processing archive opera-stable_45.0.2552.898_i386.deb (--install):
cannot access archive: No such file or directory
Errors were encountered while processing:
opera-stable_45.0.2552.898_i386.deb
gary@Desktop1:~$ ls
Desktop Documents Downloads Music Pictures Public Templates Videos
...trying again...
gary@Desktop1:~$ sudo dpkg -i Desktop/Maintenance/opera-stable_45.0.2552.898_i386.deb
Selecting previously unselected package opera-stable.
dpkg: considering removing opera in favour of opera-stable ...
dpkg: yes, will remove opera in favour of opera-stable
(Reading database ... 226820 files and directories currently installed.)
Preparing to unpack .../opera-stable_45.0.2552.898_i386.deb ...
update-alternatives: using /usr/bin/firefox to provide /usr/bin/x-www-browser (x-www-browser) in auto mode
update-alternatives: using /usr/bin/firefox to provide /usr/bin/gnome-www-browser (gnome-www-browser) in auto mode
Unpacking opera-stable (45.0.2552.898) ...
Setting up opera-stable (45.0.2552.898) ...
update-alternatives: using /usr/bin/opera to provide /usr/bin/x-www-browser (x-www-browser) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/man1/x-www-browser.1.gz because associated file /usr/share/man/man1/opera.1.gz (of link group x-www-browser) doesn't exist
update-alternatives: using /usr/bin/opera to provide /usr/bin/gnome-www-browser (gnome-www-browser) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/man1/gnome-www-browser.1.gz because associated file /usr/share/man/man1/opera.1.gz (of link group gnome-www-browser) doesn't exist
Processing triggers for gnome-menus (3.13.3-6ubuntu3.1) ...
Processing triggers for desktop-file-utils (0.22-1ubuntu5.1) ...
Processing triggers for mime-support (3.59ubuntu1) ...
Processing triggers for hicolor-icon-theme (0.15-0ubuntu1) ...
Processing triggers for shared-mime-info (1.5-2ubuntu0.1) ...
Processing triggers for man-db (2.7.5-1) ...
gary@Desktop1:~$

It seemed to install ok, but on launch, I get an error window titled "Ubuntu" that says "The application Opera has closed unexpectedly." When I click the Details button, it says ExecutablePath /usr/lib/i386-linux-gnu/opera/opera and the processing swirly took a long time. Then: Package opera-stable 45.0.2552.898 [origin: Opera Software ASA]; ProblemType Crash; Title opera crashed with SIGILL; ApportVersion 2.20.1-0ubuntu2.10; Architecture i386; CoreDump actually says "(binary data)"; CurrentDesktop XFCE; Date Sat Nov 11 16:19:28 2017; Dependencies (has a long list, won't let me copy) ... much much more including JournalErrors ACPI Warning (several) and a long list of other items; ...UnreportableReason This is not an official Ubuntu package. Please remove any third party package and try again.
Relaunch button gave same error window.

I suspect version 45 needs something my machine doesn't have - more memory, ESS2, ? - or maybe I need to change some BIOS setting. The BIOS is still configured for XP, and Opera 12 seemed happy. Is there an Opera version between 12.16 and 45 that might be more appropriate? Or can you coach me to get this one working? Thanks again for your attention to my plight.

@nikt11 when I open it, there's an install button. I click it, and it seems to react, and there's drive activity, but pretty soon it reverts to the unclicked-looking install button and never does anything more. No error message. Opera did not appear in the Xubuntu "mousehead" menu. I tried a couple of times. I'm not sure where to find an install log, if it writes one.

@nikt11 ? I just downloaded Opera for Xubuntu Linux 32 bit yesterday and got version 12.16 . It says it's up to date, but the Themes utility doesn't recognize it. Where did you find 45? The .deb installer I downloaded from opera.com didn't work, so I followed the instructions at https://xubuntugeek.blogspot.com/2012/10/hot-to-install-opera-in-xubuntu.html : cd && wget -O opera.key http://deb.opera.com/archive.key && sudo apt-key add opera.key && rm opera.key && echo "deb http://deb.opera.com/opera/ stable non-free" | sudo tee /etc/apt/sources.list.d/opera.list && sudo apt-get update && sudo apt-get install opera -y

Hello, Opera community.
I just installed Opera 12.16 on an older machine (AMD Athlon XP 1800+ 1.53 GHz, 640M RAM, used to run XP) now running Xubuntu 16.04.3 LTS 32-bit.
Firefox crashes repeatedly, possibly because the CPU does not support SSE2 CPU commands. Opera seems stable.

BUT, the Opera menu dropdowns, and browser configuration window buttons, are displayed in light green text on white, and are almost impossible to read. (Mousing over a menu item turns it to white text on blue while the cursor is there.) There's no good way to read the buttons - I've been relying on "OK" usually being the right-most button.

In Tools / Preferences / Advanced / Fonts the browser menu font can be changed, but the color control is inactive (greyed out). I can change webpage font colors, and the browser menu font color stays inactive no matter which font I choose. I'm not sure where the font color configuration is stored; I looked at .opera/operaprefs.ini and did not find it.

Strangely, no one online is reporting a similar problem. I have searched repeatedly on terms including Xubuntu Opera light green text menu text problem, etc. (Of course, few people are trying to configure a machine as out-of-date as this one.)

Can you help me make the menus readable? I can't give this machine to its owner as usable this way.