Hi,
Unfortunately this is definitely not possible, as it’s basically only an alias/redirection to an existing content through rulesets (I assume).
In the example of https://graphenstone.com/paints/grafclean-matt/ is only an “N to 1” alias to https://graphenstone.com/colours/white/ URL, and it does not actually exists as an individual post type object of any kind.
You can’t add these manually either, as a matching post type object must exists in the wp_posts table.
If there was something like an “alias” custom post type, which was used basically to reference other post type objects in a 1 to 1 relationship, then in that case it might be possible via some custom coding. (by injecting hooks to the index to fetch the referenced post type fields and index them)
I usually recommend custom codes where I can, but this is I’m afraid not possible.