This sounds great – will make it much easier to select the right pupae for dissection.  Here is the paper:

Tubby-tagged balancers for the Drosophila X and second chromosomes

We generated FM7a and CyO balancer chromosomes bearing a Tubby1 (Tb1) dominant transgene. Flies heterozygous for these FM7a and CyO derivatives exhibit a phenotype undistinguishable from that elicited by the Tb1 mutation associated with the TM6B balancer. We tested two of these Tb-bearing balancers (FM7-TbA and CyO-TbA) for more than 30 generations and found that the Tb1 transgene they carry is stable. Thus, these new Tb-tagged balancers are particularly useful for balancing lethal mutations and distinguish homozygous mutant larvae from their heterozygous siblings.