Before I4, it was split into two different Rainbow routes; R2 and R4. R2 terminates in Sandiacre along with R4, but, R4, however, terminates in Derby.
R2 and R4 got merged together to make Rainbow 4, with buses running every 10 minutes and a low floor interior.
After the big merge of Trent and Barton companies, Rainbow 4 finally got an upgrade in 2005 with more seats and real time information, powered by Star Trak.
Before Trent Barton's refurbishment, Rainbow 4 got a new name with new looks. These buses were shown in 2011, but, hit the road as the first route in the new livery in 2012.