In general, yes, the colour of the sealing disc was to be used for identification of the load. This idea was stated early on in the design concept. In practice, blue was for lead buckshot and orange was for TC buckshot.
However, there are many developmental loads which stray from the convention.
A clear blue plastic top wad was for lead buckshot. But it was also used for a TC buckshot as well as a ‘birdshot’ load.
A clear plastic top wad was used for flechette as well as various shot loads. Some flechette loads have no top wad at all.
An opaque/white plastic top wad was used for a buckshot load.
An orange plastic top wad was to I.D. the TC buckshot but was also used on other shot sizes.
Envisioned were all sorts of loads as physical size of the projectile permitted more than just shot loads - eg. shaped charge as well as KE penetrators.
I am currently collecting information for an article for the Journal. I have already received some substantial contributions. Of course there must be more out there as well as specimens I don’t have.