The Beige Clock Tower was an absolutely enormous structure, colored beige, that appeared in the middle of Net.ropolis at the beginning of Beige Countdown, heralding a coming threat...
The Tower, seemingly, first appeared as a fictional concept, in stories written by Dick Hey and Dizzy Collar, before emerging into the Looniverse.
It turned out that it had appeared before the Bryttle Brothers' previous attack, during Beige Noon, but the memory of that time had been confused.
When it first showed up in Net.ropolis, it was already enormous, and kept growing from there, seemingly absorbing sustenance from the things it decayed (see below).
Whoever or whatever touched the Beige Clock Tower would decay into dust within seconds. When the clock hands struck twelve, the Bryttle Brothers emerged into the Looniverse.
After it appeared, people in Net.ropolis grew disturbed, rioting, forming cults, and occasionally committing suicide; it's not known if this was an active effect of the Tower, or simply the stress of living next to a giant cosmic death machine.