Details on 'Servicing', in reference to guided missiles, are not in the 1964 publication on markings. This as the available PDF of that publication is missing those pages. It jumps straight from rocket markings to the plates for guided missiles.
Though not available these comments on 'Servicing' are mentioned far earlier within the said publication.
Used on certain training versions of guided missiles. In certain instances where operational non-explosive parts are used in the assembly of these training versions, the coding colour may be applied in the form of patches.
In the later similar publication 'DEF STAN 00-810 - Marking of Ammunition & Associated Packages', servicing is described as...
A training guided missile, with fully functioning mechanism similar to, but not necessarily identical with, their operational counterparts, used for testing and assembly purposes. It is not intended to be launched and has no explosive parts.
So, there you have it.