As discussed in T11093, having a consistent colorscheme would be helpful for a seamless "KDE experience".
Kdenlive shows a way to implement this in a manner that still allows a dark-themed colorscheme by default.
KPhotoAlbum could use the default system colorscheme for "normal" UI elements, and use Breeze dark for contexts where a dark colorscheme is appropriate (e.g. thumbnail view). The secondary colorscheme needs to be configurable, of course.