I sure don't see an Aluminum core. Looks 100% carbon to me. But it's strange to see the two resin shades. I'm guessing the layup was cured in 2 steps, probably to build up the inner diameter to achieve the right ID spec. I gotta say IMHO the vertical cracks at the Red and Blue arrows (second photo) look horrible to me, but if you say you can't feel anything with your fingernail on the outside, then I'll take your word for it that it's standard Cannondale layups.

The main stress-riser you have to look out for is from the base of the stem causing wear on the steerer, or over-tightening causing shear/crushing of the steerer. In both cases it should show up as marks/cracks around the stem rather than longitudinal.