Vacbear, my own memory is that all the Seniors in this colour scheme had the on/off switch set into the body of the cleaner and was the first to have such a design, despite the Junior having had this design for several colour schemes prior. I often wondered why the Senior machines did not do so until such time that they did. Also the difference between the bag on Ryry's Senior and the one in your booklet is that the latter has the original external metal bracket on the top of the dustbag, where as the former has an integrated unit. Again, something which the Junior had been using for a good deal of time, but not seen on the Senior. I do wonder if Ryry's cleaner has the spring loaded bag hook fitted to the outside of the handle like it always was on the earlier Senior cleaners, or integrated into the handle like on the Junior. Such is my memory, I cannot recall when this design was introduced to the Senior.
Your mentioning that the cleaners then shifted to blue / white, with the Junior in brown / pumpkin reminded me that during the late 1960's and early 1970's there seemed to be a medley of colours, in a way which Hoover had not really pursued before, when I think how they previously had a pink & white range, followed by grey & white, hop green & jonquil, and then the smoked pine & Swedish green we see here. After this, or even during it really, looking at the Convertible and Suitcase in your booklet, there were models in brown & pumpkin, with the Junior to follow, and the blue & white scheme being applied to the later convertible, dirtsearcher junior, and later still the new Senior with 4-position height adjuster. But heading into the 1970's, the Junior, Constellation, and 417 cylinder were being produced in a white & jade green colour scheme.
This was clearly a turning point for Hoover I think. In the late 1960's there seemed to be little desire to produce whole ranges of cleaners in one colour. I suppose it did somehow 'date' the cleaners somewhat if all models were the same colour. I am also not sure that any other manufacturer employed this mind-set of using one colour and style when it came to vacuum cleaners, though of course many did so for major appliances like washing machines and dryers in order for consumers to purchase more than one matching item in the range. Unless perhaps it was Hoover's intention that a consumer might wish to buy two cleaners in a range, such as a Junior upright and a 417 cylinder? On price alone I can't remember many people being wealthy enough to have afforded two brand new cleaners in one go, but I do wonder why Hoover produced whole blocks of colour co-ordinated cleaners.