I thought it was done as each route got new buses, under the rainbow umbrella. Things like the Rainbow 5 later became Indigo.. The 34* group, rainbow 3, now the Threes. Initial changes would have been with the arrival of the S154 UAL batch of Optare Excels, That said, the Dennis Lances N356 VRC were branded for Rainbow 4 and 5. Rushcliffe services would have been in the days of Optare Deltas, later becoming MAINLINE. The Ilkeston service would have been the Double Two, later the TWOs. In the case of the Swift service to Ashbourne, that was probably the last of the Excels. It all seems so long ago.