F1 2020 Question for mod

[flo2pac]

Hello I would need your help regarding the modifications I would like to make on the original files like "paint.d.tiff" or numbers. As soon as I change I always have a white background color as I show in the image below and I would like to know in which DDS format should I save my file from photoshop? For example "color" or just "color + alpha" because even while recording in "color + alpha" I have this frame. Can you help me please? thank you