The arms installed by the CIE S&T department were slightly tapered outwards towards the end as Compound recalls. Reflective surfaces were used towards the end as required for sighting purposes. They had quite a distinctive look and were unlike anything in GB or NI. They were all lower quadrant.
As the direction for GB distant signals to be yellow took place after independence, it was not applied as a requirement south of the border. CIE signal arms were not distinguished by colour in the way that British ones were, and they went even further their own way when reflective surfaces started to be applied to some of them. Distant signals in NI followed suit with GB and converted to yellow distants with a black chevron. As for the companies like CDR, Swilly, DNGR and so forth I, often wonder what colour their lower quadrant distant arms were as the photos are usually black and white. For instance, what did the GNR(I) do on either side of the border? The Sligo Leitrim just dotted various ancient designs of signal around as they took the notion.
The reflective coating applied to some CIE distants and gate signals was a yellow/orange shade on the outer section beyond the white chevron. The yellow outer and red inner reflective coatings were a bit pearlescent and seemed to be slightly different shades in certain light conditions. Apart from the outer portion the rest of the CIE distant arm remained technically red, but the red reflective version had an orange or pink look under certain light. Reflective home signals would also be different shades of red as only the inner part might be reflective (I would post a photo but I cannot get it to work).
NIR also used reflective coatings in some cases to improve conspicuity. The down distant at Dunmurry was an early one to have a reflective coating applied. That definitely looked yellow and black to me in all light conditions.
CIE shunting signals were generally round discs apart from some ex-GNR(I) rotating ones and some really old rotating indicators (as at Loughrea and Dunsandle for instance).
Gate signals generally followed the distant fishtail pattern with the stop board mounted on the gates, but some were fully signalled on busier lines. At the other end of the scale were ancient double armed gate signals on the Burma Road, the North Kerry and elsewhere.
So the vast majority of Irish mechanical signals were lower quadrant semaphores. Exceptions were the somersaults on the NCC, plus the few upper quadrants as noted. Then there were the Sykes banner signals on the Bangor line, one platform starter at GV St in Belfast, and a few other places. The UTA also put one somersault signal in at Queens Quay. The NCC was responsible for signalling policy on the CDRJC, though it remained standard lower quadrant territory. However, I seem to recall that the starting signal at the old CDR station in Derry (which was pulled off when the business which used the site in the 1970s was open) was a somersault. That is getting a bit off topic.