Different countries such as China, Taiwan and Japan have different classification system. Japanese classification in strict accordance to Rikkoku Gomi, does not grade based on resination appearance but on specific scent profile as per the incense house specification.
There is no colour coding in Japanese Kyara classification, at least you will not find such colour system for Kyara in Shoyeido and Yamadamatsu. Hence it is technically not right to equate shin kyara to white kyara. ‘Shin’ translate as ‘new’ simply means young or immature kyara. You can read more about Shin Kyara in KZ article.
https://www.kyarazen.com/hon-kyara-versus-shin-kyara/
On the other hand, the Chinese grade the kyara not just in terms of smell but also by the state and formation of resin in the kyara wood e.g whether the resin was formed and amalgamate with the wood fibers while the tree was still alive or not. The colour classification can be viewed as either an association to the different kyara formative states or for ease of marketing purposes depending on who you are talking to.
Personally I do not agree there is an order to the colour in terms of quality but rather each colour reflects one aspect of the kyara scent spectrum. In my opinion, the price differences between each colour (white is more expensive than yellow by the way) is simply due to the scarcity of the material rather than quality itself.