If you'd like to change the style of the input fields in Identity Management templates, you can do so by adding the below CSS to the Identity Management Layout template.
.placeholder {color:red}
This will change the style of all input fields. If you'd like only to update selected fields, you can do so for example by using the following CSS code.
For the email input field add:
.icon-email + t {color:red }
For the password input field add:
.icon-password + t {color:red }