Design style

In my collection of Norton related books there's a lot of information about mechanical design development, and mechanical designers.  But as far as I can see, almost nothing is written about who developed the design styles.

I assume that frame design was entirely a matter for the chief engineering designers: Moore, Carroll, Franks, etc.  Likewise engines.  But who was responsible for the development of changes in oil and petrol tanks and their livery, which changed almost every year or two through the 30's,  and again in the 50's?  Who designed the Slimline tank badges? And the variety of Commandos?  He or they seem to deserve some credit, but never had any.