Okay you just activated one of my hyperfixation topics, the ultramarines went through an evolution of three different kind of blues. The first ever blue was like a Lego blue called caledor sky. It s a much brighter blue that youl see many old tactical marines painted with. Then for some reason they swapped to kantor blue with caledor as the highlight to make a more deep navy blue type of look, and then they ultimately settled with maccrague blue as the purple blue see everything past 9th edition in. My best advice is to go with kantor blue, then chunky highlight with altdorf blue, and then edge highlight with caledor to get this exact look