Hi Michelle,
You could accomplish this by using the Rich Text editor in the form designer. In Field Settings, highlight the field label then in the right sidebar click on the pencil icon to the right of the label. This will open up the Rich text editor where you can apply color edits.
You could also go to the Form Settings tab on the left sidebar and click on the Themes tab. Next click on the gear icon in the upper right and choose the cusom css option. Add the appropriate CSS changes here and save. You should be able to target the form using this property: form .mktForm
Hope this helps,
Best,
David