Can I change the text size and color on hint text?

Yes, you can increase the text size and change the color by injecting the following CSS code as explained on this guide: http://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes

.form-description-content { 

    font-size: 20px !important; 

    color: red !important; 

} 

Example:

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