Which input field option is better from a UX perspective: with gray placeholder text or with a bold black header inside?

Using a bold black label above the input field is generally preferred from a UX perspective for several reasons:

• Constant visibility: The label remains visible even after input begins, helping the user remember what to enter.
• Accessibility: For users with disabilities and when using screen readers, a bright label is more understandable.
• Avoiding confusion: The placeholder disappears when typing, and if the user gets distracted, they might forget what to input.

Gray placeholder text is better used as an additional hint rather than the sole way to indicate the field.

Example of good markup:

<label for="email" style="font-weight:bold; color:black;">Email</label>
<input type="email" id="email" placeholder="example@mail.com">

Thus, it is better to use a bold black label above the field and, if necessary, additionally a placeholder for input example.