The IDE that comes to mind, per your language requirements, is Eclipse.
I have only really used Eclipse for Java development and while it has its annoyances, it has gotten a lot better over the years. It may not live up to Intellij for some people, but overall I am satisfied with it. In general Eclipse is a platform with all of its functionality built as plugins (or plugin-like things. I am not 100% sure how it's structured). The Java Development Tooling (JDT) is bundled with the default install, and has all you would expect from Eclipse. For C and C++, there is the C/C++ Development Tooling (CDT) plugin. I have not used it, but appears to be just as feature complete as JDT.
As for your other three requirements, Eclipse allows you to customize the editor from its Preferences panel. Once you are in the Preferences panel, in the navigation tree to the left you can follow "General" to "Appearance" to "Colors and Fonts" and customize how you see fit. One nice feature about the "Colors and Fonts" preferences is that when you click on preference it will preview it for you before you apply it. While you can customze the base colors and fonts, you can also customize the syntax color schemes on a per-language basis. At least for Java, if you navigate from "Java" to "Editor" to "Syntax Coloring" there is a point-and-click interface for changing most aspects of the syntax color scheme.
To be honest, I don't know if these features are "easy" for someone visually impaired to navigate and use, but overall I have found them fairly intuitive. I have not needed to consult a manual or some other obtuse configuration file in order to change the settings to my liking.