Change text color

I know this should be ridiculously easy to do.
I’d like the heading of each text prompt to be white (instead of the current grey )
I.e.
“name” , “email address” etc (not the input text that a client may enter).

I’ve currently got the contact form as a black background, and I know that it must be a matter of changing some bit of CSS to get this text to be white, but I’m not sure where this should occur.

Kind regards,
Danster

https://wordpress.org/plugins/contact-form-7/