You should be able to fix this by re-downloading iTunes 12.3.2.25 from http://www.apple.com/itunes/download/ and re-installing. The flashing/flickering iTunes Store screen was present in the original version of this release (from Dec. 9) but Apple sneaked out a re-build (unfortunately and misleadingly with the identical build number) on Dec. 23/24 that seems to fix it for most/all users.
There is another - possibly related - issue that affects the iTunes display on very high resolution monitors. This first appeared in iTunes 12.3.1 but has not yet been fixed, though it can be mitigated by reducing the size of the iTunes window.