On closer inspection, there are actually a few things to address here. 1) by convention for Infusion we distinguish between classes that are used for styling (fl-) and those used for selectors in javascript (flc-). Meaning that styling should not be applied to flc- classes, and fl- classes should never be used as selectors. You might want to consider using a similar scheme to avoid confusion and ambiguity. 2) I'm not sure why you need to be adding and removing multiple classes from each. Can you simplify this a bit? 3) The styling related classes you are adding/removing should be defined in a styles block in the component's options. This will allow for an integrator to more easily override it.

```javascript
    ...
    styles: {
        defaultTheme: "fl-theme-uio-default",
        contrastTheme: "fl-theme-uio-yb"    
    }
    ...
```

4) for the actual toggle you probably need some sort of wrapper to do the switching.


All of these together might look something like the following.

```javascript
(function ($, fluid) {

    fluid.defaults("gpii.uiOptions.enactors.contrast", {
        gradeNames: ["fluid.viewComponent", "fluid.uiOptions.enactors", "autoInit"],
        preferenceMap: {
            "http://registry.gpii.org/common/display.screenEnhancement.highContrast": {
                "model.value": "default"
            }
        },
        styles: {
            defaultTheme: "fl-theme-uio-default",
            contrastTheme: "fl-theme-uio-yb"
        },
        invokers: {
            toggleContrast: {
                funcName: "gpii.uiOptions.enactors.contrast.toggleContrast",
                args: ["{that}.container", "{that}.options.styles.defaultTheme", "{that}.options.styles.contrastTheme", "{that}.model.value"]
            }
        },
        listeners: {
            "onCreate.toggleDefaultTheme": {
                listener: "{that}.toggleContrast"
            },
            "onCreate.toggleTheme": {
                listener: "{that}.applier.modelChanged.addListener",
                args: ["value", "{that}.toggleContrast"]
            }

        }
    });

    gpii.uiOptions.enactors.contrast.toggleContrast = function (elm, originalClass, contrastClass, enableContrast) {
        elm.toggleClass(originalClass, !enableContrast);
        elm.toggleClass(contrastClass, enableContrast);
    };
```