As Adrian Grygutis pointed out on the comment, in 1.0.0, TextField has a parameter colors. You could customize your TextField by calling TextFieldDefaults.textFieldColors(...) with the parameter you want to change.
TextField(
    ...
    colors: TextFieldColors = TextFieldDefaults.textFieldColors(textColor = Color.White),
) {
As for theming, and if you want to avoid calling every time:
ProvideTextStyle(TextStyle(color = Color.White)) {
   TextField(
       ...
   )
}
You could create a composable with your own set of TextFieldColors and add it as a parameter in your TextField. You could for instance, have all colors as white:
@Composable
fun MyAppTextFieldColors(
    textColor: Color = Color.White,
    disabledTextColor: Color = Color.White,
    backgroundColor: Color = Color.White,
    cursorColor: Color = Color.White,
    errorCursorColor: Color = Color.White,
    ...
) = TextFieldDefaults.textFieldColors(
    textColor = textColor,
    disabledTextColor = disabledTextColor,
    backgroundColor = backgroundColor,
    cursorColor = cursorColor,
    errorCursorColor = errorCursorColor,
    ...
)
To avoid calling this in every TextField, you can then create a custom MyAppTextField for your app that calls the default TextField with your custom TextFieldColors as a default parameter:
@Composable
fun MyAppTextField(
    value: String,
    onValueChange: (String) -> Unit,
    modifier: Modifier = Modifier,
    ...
    colors: TextFieldColors = MyAppTextFieldColors(),
) {
    TextField(
        value = value,
        onValueChange = onValueChange,
        modifier = modifier,
        ...
        colors = colors,
    )
}
That way, you would only need to call MyAppTextField. It's a good way to override colours inherited from the theme if needed.