I am only familiar with oxy-acetylene, but you say that when you
changed fittings (tips?) with another torch you got a blue flame,
which went orange over time. The blue flame is the result of a good
mix of oxygen with the acetylene before the mixture is ignited at the
end of the torch tip. You say you got the blue flame when you first
used the new fittings, so your fuel/air mixture is probably good.
Another characteristic of acetylene is that when incompletely burned,
it produces lots of soot. I suspect that the hot tip is accumulating
soot just inside. Particles of soot will blow out with the gas/air
mixture and cool your flame, making it orangey. Other than adding an
oxygen tank or cleaning your tip before each use, I don’t know what
you can do to stop this.