We studied the emission properties of fluorene-based conjugated polymers blends as a function of composition and preparation conditions, namely the addition of an additive, 1,8-diodooctane, DIO. We combined a blue, a green and an orange-emitting polymer, whose frontier levels energy alignment ensures an efficient energy transfer. We found that the addition of DIO partially suppresses the energy transfer process, which we attribute to changes in the blends films phase separation details. In particular, we found this approach is effective at generating white light-emitting diodes and propose this to be a process that may be used in other systems.