Written

You can see a demonstration form using CFv3 by clicking here {rokbox text=|here|}http://greyhead.net/index.php?option=com_chronocontact&tmpl=component&chronoformname=placeholder_label_demo{/rokbox}.
The code to do this is quite complex and I have written a tutorial document explaining how to do this in both CFv3 and CFv4 that you can buy for a few dollars from my site here {rokbox text=|here| size=|1000,600| }http://greyhead.net/how-to-docs/chronoforms-placeholder-labels{/rokbox}. The download package includes sample forms that you can restore to your site.
ChronoForms v5
ChronoForms v5 has an option box for a Placeholder Label in the element configuration.