To further aid the selection of a favorable dye for the blue-green FRET, the cross-talk intensities of the dyes B1, B2, B3 and B4 are plotted relative the fluorescence intensity of the green at the respective excitation wavelength (fig. ). B2 turns out to be the most favorable FRET-partner for the green dye, since at 422 nm excitation the emission from the blue dye is 9.5 stronger than the emission from the green dye at the same excitation wavelength. blue Bodipy to the green Bodipy and then to the red Bodipy in a cassette type fashion. The individual emission spectra of the blue, the green and the red Bodipy (fig. ), show that 423 nm excitation also leads to significant direct excitation of the red Bodipy and consequently to red cross-talk emission, while the excitation of the green Bodipy at 423 nm gives rise to a weak cross-talk fluorescence signal.