With US certificated turbine aircraft, there is no caution range (yellow band) because.....that is what the regulations say. However, when piston aeroplanes are re-engined with turbine powerplants, the Vne, which now becomes Vmo is sometimes reduced...but not always.
Recall years ago someone re-engined a C207 with an Allison turbine, and flew it very near Vmo all the time....until the wings came off over Mt. Wilson in southern California. The investigation revealed greatly elongated holes in the wing attach fittings.
