The problem I was facing is the opportunity to change the background in fields in a model driven app. Unfortunately, there is no easy way of doing that rather than implementing a PCF. The PCF in this solution allows to update the background color of a text field. Each one has it's own solution.
You can find a short introduction on the PCF Gallery here. Solutions to be downloaded here There is not a managed solution for all PCFs right now. I am working on those and continuously update the repo.
Make sure to download the .zip as you have to import it like every other solution into your Power Apps.
Import the solution into your environment. If you have a textfield inside your form - go to the components tab while you are in edit mode and use the InputFieldToChange component. If you cannot find it in the popup make sure to have a look in the search for more components tab. Once you can select it make sure to tick the show component on fields and add a rgb(xxx,yyy,zzz) value in the Static value field. For now only rgb works - no hex or hsl colors.
Apply the changes and you will see the color in your field:
You will find an additional field with the language selection. Type in EN-en or DE-de as english and german are currently suppported as yes or no. The field cannot be applied to choices, only Yes/No fields.
If you encounter any problem or wish more extension feel free to message me via LinkedIn