Any of our gantry based templates have the ability to use presets. In general most will allow you to change all the colors you need, some offer more control for colors than others, but I would think the vast majority would fulfill your requirement.
all you need the so to change preset in the front-end is have a link to your site with ?preset=presetname where presetname is the name of your preset that's it. So, once you have save a preset with the high contrast colors and save that as a preset then you can easily switch to it in the frontend.
If you have need to reset the preset in the frontend then you append ?reset-settings to your domain url.
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