Please see the following image
The project is currently running in Visual Studio and debugger point has been hit. When I hover over "IDs", it shows a pop up(in black). I want to increase its font size.
I've tried several options in Tools -> Options -> Environment -> Fonts and Colors, but couldn't get it to change.
You're almost there:
Tools -> Options -> Environment -> Fonts and Colors -> Show Settings for -> Data Tips
(requires restart of Visual Studio to take effect)