Wow! Those pics show some serious potential for a fascinating layout, Davy; and welcome to here. There are many with superb skills and knowledge who can help you.
Regarding liveries, the main livery by far was battleship grey, perhaps marginally darker than your illustration. It is important to note that chimneys and smoke boxes were grey as well, as were most can interiors, and motion inside and out. Numerals were in a dark cream or light yellow, and "snails" were in the "Eau-de-nil" colour, which was a very pale yellowy green. Snails were never yellow or cream, always eau de nil. Some tenders were in service without snails, either because they hadn't been reprinted from late GSR days, or they just hadn't had any transfers handy.
Very very few locos were black, and those that were would have been painted that way from about the mid fifties on. There is a list in Bob Clements book about CIE steam of what engines were green or black. These were with probably a single exception the only locos with black chimneys and smoke boxes, though Cork turned out a solitary J15 as late as about 1960 in grey, but with black smoke box. All green locos were fully lined in black and white, and the exact details can be seen on 800 in Cultra. One 800, I think 802 from memory, got a somewhat lighter shade of green in the early 50s, and at the same time became the only CIE loco to carry a red background on its number and nameplates - the other two had blue, again as on 800.