Funny thing: the 'black screen issue is actually white if you use the "light" theme for Windows Phone 7. But that's not really what you want to hear, is it? You want to hear that Flickr finally manged to get rid of one of the most pesky bugs with their otherwise sweet app: the blank screen when launching. (Which we thought was fixed in v1.3...har har)
Well, good news is v1.4 is now live in the Marketplace and it address exactly that problem. Having tried it ourselves, we can vouch for its authenticity--it really just works now. So go ahead and grab the update or hit the link here in case you want to re-install. And if you don't care for their official version, we have to give mad props to the 3rd party app Flickr Manager, which is even better in some ways (e.g. viewing your stats). Grab that app right here.
Thanks, deeper2k, for the heads up