Can't change fonts etc. in Preferences.txt

I'm using the IDE on Windows 7. I am somewhat vision impaired and the editor's grey font doesn't do it for me. I know about Preferences.txt and have used it to change the default window size, but can't seem to manage to change the font. I tried

editor.font=Monospaced,bold,26

But no boldfaced. Also no way to change the color.

Similar problems with colors on one-line and multi-line comments, variables, etc. No colors at all here.

I've done a lot of Googling, and see references to theme and other options, but I don't see them at all. I'm guessing they refer to the Windows 8-10 installation?

I've had older IDEs for years, so I thought maybe the installer may be picking up settings from older versions. I just uninstalled the IDE, deleted every file and folder I could find, and re-installed the IDE.

No Joy. Can anyone helo me?

JCrens:
I tried

editor.font=Monospaced,bold,26

But no boldfaced.

The problem with the font style part of the editor.font property in preferences.txt being ignored has been reported to the Arduino developers:

Unfortunately, there has been no solution found yet.

JCrens:
I've done a lot of Googling, and see references to theme and other options, but I don't see them at all. I'm guessing they refer to the Windows 8-10 installation?

Nope. You can edit the theme no matter which OS you're using, and the procedure is the same. This is the way you can get control of colors and fonts of many of the elements of the Arduino IDE. I have attempted to document all the theme properties that can be edited, and where they are found, here:

That repository also contains a dummy library with example sketch that can be used to test how the various settings of a custom theme look. After reading over that documentation, let me know if you have any questions.

Keep in mind that changes you make to the theme will only take effect after you restart the Arduino IDE.

One thing I have not gotten around to documenting in that repository is that there is a cool new feature that allows you to save custom themes to your sketchbook folder. This is really nice because if you spend a lot of time modifying the theme in the Arduino IDE installation folder and then update to a new version of the Arduino IDE, all your work on the theme will be lost! I don't want to overwhelm you with information now so come back and ask me for instructions on this subject once you have your theme customized as you like it.

I also have a collection of Arduino IDE themes, in case you want to see if any of them happen to meet your needs:

There is another popular 3rd party theme here:

The theme files are located under a subfolder of the Arduino IDE installation folder.

Windows or Linux: lib/theme

That's my problem: My installation has no lib and no theme folders. Here's my entire folder structure:

C:\Users\DrJack\AppData\Local\Arduino15

library_index.json
package_index.json
package_index.json.sig
preferences.txt

Clearly, some important things missing.

You're looking in the wrong place. The Arduino IDE is not installed to C:\Users\DrJack\AppData\Local\Arduino15. That folder is only used to store configuration data and hardware packages installed via Boards Manager.

The Arduino IDE will usually be installed somewhere like C:\Program Files (x86)\Arduino. If you have a shortcut (maybe in your Start menu) that you use to open the Arduino IDE, you can right click on it, then click "Properties". The IDE installation folder will be shown in the "Target" field.

Yep, I just figured that out. I thought I'd deleted everything before I re-installed. I'm going to do it again just for good measure, to get a clean installation, but I see the files I need now.

Many thanks to all who offered advice. It's much appreciated.