I provide watermark versions of my clients apps for them (they're transparent PNG files with no background at all). I provide them with a "normal" version, a dark version and a white version- which covers them for everything.
Provided they/you have something like that, my clients mainly use an app called "Phonto".
Please be aware that you can't just use any image/font you like for a commercial brand or logo, everything has to be licensed properly before you can use it for a business application.