Change the color of a form field

[Aetius]

Hello!

When building a form the fields come with a default color. I want to have that color changing to neutral white,  when someone fills out the form,  thus the writing on the field can be clearly read. How do I do that ?

I have asked for the last few weeks this same question, but sadly,  until this day have got no reply. Could someone let me know if I am posting this question on the wrong forum and if affirmative, which would be the right one?

Thank you much