Upgrade to Contact Form Pro version in order to enable this feature.
Follow the next steps in order to change Contact Form input fields color easily via WordPress admin dashboard:
1) Go to the plugin settings page and open "Appearance" tab;
2) Find and enable the "Style options" checkbox.
3) Find the "Text color" section and make necessary changes in the "Placeholder color" field.
4) Save changes.
This article related to Contact Form by BestWebSoft plugin
Additional resources: Contact Form - User Guide
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