Why put in new semaphore signals? Why not put in multiple aspect signals?
Cost apart, IIRC there is a policy against replacing individual semaphores with colour lights because it is potentially both confusing and dangerous - because of the risk of "reading through" to a (more powerful) light beyond a semaphore.
Back in steam days, the LMR and SR both replaced semaphore distants with colour lights further out to allow for higher speeds (a semaphore might have needed to be motor worked anyway...); you could replace
all the running signals but to little advantage.
OT: ISTR it happened at Crewkerne, in the down direction only, but that had something to do with the distant signal for Crewkerne Gates also needing moving...