I'd suggest the color is what was (and may still be) called "International Orange." It is kind of a cross between DayGlo and non-flourescent orange. Here's something I found on the net:
"The exterior surfaces were painted dayglo to assist observers focusing on specific components under test. 203 was the only Arrow ever to sport the Canadian Commonwealth flag ("Red Ensign") marking on the tail."
In this case, contrast the wing panels to the Maple Leaf's obvious red. Certainly this color shown here is something other than crimson. Period fotos of the prototype Arrows show a color that is not red, but orange. Again, my vote is in for I.O.
Its yet again one of those things to get sorted before painting begins, if ultimate accuracy matters.