I think this deserves its own thread. Please see https://www.railforums.co.uk/threads/colourblindness-and-engineering-drawings.207171/The only signalling diagrams that use colours other than black and white are those involved with the commissioning of new works. If that were a new works diagram, green would mean that the lines/equipment were being removed, and red would mean new lines/equipment being built (With blue for those awaiting a decision). No yellow in any diagram as it can easily be overlooked, especially in low light. We don’t otherwise use colours on standard signalling diagrams, instead signals are represented using specific symbols and can be read by a trained member of staff regardless of any colour blindness (Though, that may prevent you passing a medical depending on its severity).