My Acro-II (under construction for a long long time) and a friend's KR-2 are both held together with West Systems. It has been around in the boat world for many years. Technically, it has a bit lower glass-transition temperature than many other epoxys, but is a really good general purpose epoxy. It flows better than the rather thick T-88 but T-88 seems to penetrate on glue joints almost as well as Resorcinol. T-88's only (minor) complaint is that being a 1-1 mix, it contains inert fillers. No Epoxy is 1-1 resin to hardener. Folks have always liked the West System's pumps as they make the mixing simple and consistent. I have noticed that as West hardener 206 ages a couple of years it turns brown. West Systems say that the chemistry isn't affected, it just looks dark. But I don't think that even my most elderly 206 hardener would darken a glue joint enough to call it brown.
The Weldwood Urea resin glue has been FAA approved, but is generally considered as surpassed by the Epoxys and Resorcinal. It's not a bad glue however. It has a long history and the mixing is easy. it wouldn't typically leave a brown joint.
The original AcroSport-II book and plans recommended Forest System Laboratory FPL-16. This was a light brown epoxy that might have been used in your plane if the glue lines are brown. I read the reports on FPL-16 as it was run through mil-spec tests (one of the few epoxys at the time to do so) and had excellent properties other than the normal epoxy weakening at high temperatures. It was fairly scarce and expensive, but as it was recommended on the AcroSport plans, it may have been used. The brown glue line hints at it. I haven't used FPL-16 myself, but have heard the light brown colour mentioned.
I am currently building new spars for my Taylorcraft and I am using Resorcinol. It is currently made by Bordon but has been marketed in the past by both Weldwood and Dap. Official name is Cascophen G-1131. it is the best of the FAA-approved glues for wood joints. If your glue lines are dark brown or purpleish-brown, then it is probably Resorcinol. The Resorcinol joint will be quite dark brown where I have heard that the FPL-16 joint will be more of a tan brown.
Having used both Epoxys and Resorcinol, I am a fan of Resorcinol. It doesn't have the heat problems of Epoxy, and it doesn't have the water problems of the casein glues. You do need a good scale to get the 5:1 weight ratio. If I had to splice a spar I would use Resorcinol over any of the Epoxys.
As always, corrections are welcome.