The Z80 had bulk memory write instructions that could be used to set contiguous memory addresses with the same value. You just needed to write the 32 bytes of c

The Z80 had bulk memory write instructions that could be used to set contiguous memory addresses with the same value. You just needed to write the 32 bytes of character attributes, so the change is doable while the TV ray is jumping to the next scan line. The timing was solved by setting interruptions synchronized to that instant.