The yolk color is a pigment found in vegetable matter carotenoids. For carpenter ants (and some others as well) the pigment would come from the honeydew they harvest from aphids and/or scales , many of which they've chewed the wings off of and pretty much "domesticated", or trapped into a "farmed bug". Probably also in the insects that they also eat that have also fed on vegetable matter containing carotenoids. There's almost the same amount of protein in the yolk as the white.
