I presume that you are in a "Unit" and there are other "Units" which still have the original "handsets" installed.
Is it possible to inspect one of these 'handsets" to see how it is wired and the colours of the wires concerned ? (However, this may not guarantee that the "handset" in your "unit" was wired in the same way.)
but that won't help with the colour code used in the units concerned.)
Each one of the above files contains the following
IMPORTANT NOTE :
1) Before replacing the handset make note of the wires to each terminal on the existing unit (an easy way is to cut each core off leaving a piece of the insulation in place with colour visible) twist unused cores together (so you know they are not used, do not short them out).
2) Some older systems will have cable with one coloured core and a solid white core in this case mark each core with a marker or tape.
3) Some systems may have loop on wiring, you will have 2 cables into your handset (make sure any joins remain, as these may be serving other flats on the system).
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