Orange Armor gets it's armor value from the 'armoring' mod you slot in. If you exchange it for something better, the armor value increases along with the stats.
It's always the first mod in the list that determines the intrinsic properties of the orange items (e.g. armoring on armor, barrel on guns, etc.)
Hope that helps.
I think the OP got that mechanic, what he/she is referring to is that light armor with an AR of 50 has lower Armor than heavy armor with the same AR. The question was if this applies to Orange gear as well, as in, light orange gear with an armor mod with AR 50 has lower armor than a heavy orange amor with the same mod applied to it, which I believe is the case.