For some reason the File Picker dialog has a dark background. All other dialogs are presented using standard OS objects.
It seems odd that the File Picker is rendered dark when all the other dialogs, such as Inspector, are not.
Adobe and a bunch of other graphics programs present grey text on a dark background. I'm aware that the rationale in those cases is to avoid contrast with the image. If you're working in a dark space, a white dialog is like having a torch shining in your eyes. I can't see how anyone could seriously propose the same rationale for FMP when the rest of the dialogs are vanilla OS. I'd hazard a guess that there are a few designers out there working in dark space. The rest of us are working in light space where the bulk of the day-to-day business workspace is built. For us, the dark text situated on a dark background is unreadable, because of the contrast with all the white or light themes!
If FMP was serious about offering the "right" dialogs they'd offer a switcher that toggled through light, mid, dark.