Blue being the colour of Munster in the GAA, with all-ireland semi or final colour clashes teams usually wore their provincial colours (as provincial champions) in those days. https://twitter.com/fiona_forde_irl/status/1322089607169789954

In the GAA, provincial colours more or less match the predominant colours of the official provincial flags, so Munster blue, Leinster green, Ulster yellow, and Connacht white (blue is as predominant as white on Connacht flag, but more predominant on Munster flag).

So for example when green and gold Munster champions Kerry played green and gold Leinster champions Meath in the 1986 all ireland football semi, Kerry wore blue with white trim and Meath wore green with white trim: Same with Meath-Donegal in 1990, latter wore Ulster yellow-black:

PS here are the four official provincial flags (above from left, Munster and Connacht, below from left, Ulster and Leinster).

ENDS :-)