Yes, a lot to discover!
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I had considered whether the block alternate-colour-choice/change-on-cab-selection would be better operating before, during or after the NX process.
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I discarded the during first as already said to avoid duplicating an existing process.
Second the after as one would need to work out/keep track of which blocks have just been NX allocated but not yet cab allocated. As you have touched on in order to apply the cab-specific alternate colour only to them and not to any other routes already allocated (to other cabs). Although it would have the advantage that the additional state of NX-but-not-cab-allocated might be shown.
I felt doing the colour choice first meant minimal LogixNG and no interference with the existing NX process.
