The single loco with the yellow buffer beam, C203, was even more of a livery oddity than you'd think - on next repaint, it went back to red! It was not just a one-off, but short lived too.
So, for a C, you've got:
Silver (1955-63; ALWAYS very heavily weathered!!)
Green with mid-waist lighter green line (approx 1959-1964)
Green without mid-waist line (approx 1959-64)
All black (with white front flashes about cab windows) (1962-68)
Above with yellow panels (Approx 1964 - 70)
Above with yellow panels and yellow buffer beams, as long as it's C203 (around 1963/4)
Black'n'tan with full tan lower (1963+ / short lived, only on a few engines)
Black'n'tan with dipped tan lower (after re-engining; thus suitable for 1970s, not 60s) (1972-7 approx)
Supertrain (1972-86)
No C class locos ever received the first IE "Tippex" livery, as the last were withdrawn about a year before it was introduced.
It should be noted, as will be seen from dates shown, that within the 1962-72 period, a number of variations of the black'n'tan (or black!) livery were concurrent. This was also the case with the A, B101, D, E and G classes; some having black liveries and some with tan as well. The dates shown above reflect the periods within which the liveries quotes would have been seen, in some cases on a loco which hadn't seen a paintbrush in a while (a bit like dome of the very scruffy 071s in black and silver in recent times!).
The reason that some locos had tan and others didn't was meant to be a bit like the distinction between lined green and all-grey on steam engines. Lined green was for passenger locos and Dublin Suburban locos, with grey for everything else. The all-black was initially supposed to be for goods and shunting diesels, with mixed traffic and passenger locos being black'n'tan. Shunters for Heuston Passenger would gain tan too, hence many D and E types bearing this (though latterly - certainly from about 1974 - the E's were all black without exception). Bizzarely, some of the G class had tan as they operated passenger trains on the Loughrea line!
That was the theory, but in practice it was mix'n'match...