Edit Color, Background Color, Font Style, Font - Weight, Font Size and Font Name of Placeholders with the Contact form 7 placeholder styling addon of UACF7 (Ultimate Addons for Contact Form 7)..
See the two Form's Placeholder below for example. You can see both form's placeholder style is different.
Glimpse of Backend Editing Panel (Click to Enlarge)
What if you could design all forms from one place?
Completely style all your Forms without a single line of css code & from One Place. Styling all forms placeholder text (e.g. color, background color) without writing any css code.