According to Lillie (1990) Sudan Black B has two secondary amino groups that which allow it to interact with tissue, where as Sudan IV is a stain for fats. Hope this helps
Lillie (1965 edition) has a nice table listing "Oil soluble dyes used as fat stains". Sudan 4 is a red dye and Sudan Black B is black.
Sudan 4 (which you do not have) gives similar staining to Oil red 4B and Oil red O) (both give red staining).
I have used Oil red O ages ago on frozen sections of human aorta, the fat staining was deep scarlet.
I have copied a method from an old paper (1989) for Oil red O (rat aortas): https://ac.els-cdn.com/0014480089900026/1-s2.0-0014480089900026-main.pdf?_tid=0bc07e0f-8b69-460f-871d-914ab3e6ab23&acdnat=1528982881_24329351ab4ea2814ffb3a78b198d46d
Staining Solution A saturated solution of OR0 was prepared by slightly modifying the method of Lillie (1944). OR0 (0.3 g) was dissolved in 10 ml of 2-propanol (Fisher Scientific) and filtered through a Whatman No. 1 filter paper (stock solution). The working stain was prepared by diluting the stock solution with distilled water (6:4); before use it was passed through a 0.2~um Acrodisc filter (Fisher Scientific). Staining Procedure and Light Microscopy Each segment was gently cleaned of adventitial tissue, rinsed in distilled water, quickly rinsed in 70% isopropyl alcohol, stained for 30 min, rinsed again in isopropyl alcohol, and returned to distilled water. The segment was bisected transversely; each sample was cut open along one side and laid flat on a glass slide, intimal side down; and the adventitia was carefully cleaned of visible fat. The sample was then mounted in water, coverslipped with the endothelial side up, and studied en face. Frozen cross sections of ORO-stained samples were cut with a microtome (American Optical Model 880) equipped with a freezing apparatus.
You can use Oil Red O isopropyl method to en-face stain whole aortas followed by macro-photographs and quantification (percentage of whole area occupied by staining)