provide your website url here or pm it to one of the staff.
Most probably it is something that @EricF and @Jailer has mentioned. Check if you're using white logo on white background, or black on black background.
My site is https://www.gummyimages.com but I managed to fix it somehow....... I'm still not sure what the exact issue was. It was probably one of the following:
forgot to set my file name as logo.png (or whatever ext it was), uploaded it to the wrong one (there was 2 options in dashboard where u can upload logo). Anyway, this has been resolved.