Cross references: Red Nucleus Red Nucleus Evolution
Heme Globin Myoglobin Myoglobin Evolution
Cerebellum Red Nucleus Cerebellum Muscle Innervation
Motor Neuron Evolution Motor Nerve Organization
Fast vs. Slow Twitch Muscles Shark Muscles
Searching Google for "red nucleus color" yielded 5,180,000 claimed hits. I scanned the first 8 pages without finding any mention of Globin or Heme or anything else related to Myoglobin . The few authors who mentioned the color said that it was pink when it was fresh, and it was also said to be highly vascularized and rich in iron. The following three references are from this 8 page search.
1. Brain Stem - Brain Stem.pdf
Site down the last time I looked.
2. Mesencephalon - Red Nucleus flashcards
Red Nucleus Input: Cerebellum
Red Nucleus Output: Rubrospinal Tract "
Both hemoglobin and Myoglobin contain iron. Since iron oxide (rust) is red, one of these could be the source of the "pinkish color in fresh Brain specimens".
3. Anatomy Atlases: Atlas of Microscopic Anatomy: Section 1
So, perhaps the red nucleus is "red" in name only? Perhaps it gets its freshly cut redness from hemoglobin. Is there any reason to rule out Myoglobin ? If it's myoglobin, then perhaps the red nucleus is "red" as long as it's intrinsic myoglobin is oxygenated. I searched for "red nucleus myoglobin" to see if the red nucleus contains or includes myoglobin. Although Google claimed 1,380,000 references, I did not find anything helpful when I looked at the first 4 pages.
Searching Google for "red nucleus iron" yielded 5,290,000 claimed references.
Higher iron in the red nucleus marks Parkinson's dyskinesia. - 2012 (Goog)
No indication whether the iron is metallic or in an organic complex.
Brain iron deposition in Parkinson's disease imaged using the PRIME magnetic resonance sequence - 2000 (Goog)
Wrigglesworth and Baum, 1988). However, it is also associated with the production of damaging free-radicals, which may lead to neurodegeneration via lipid peroxidation.
Brain iron is stored in the protein ferritin (Hallgren and Sourander, 1958; Griffiths et al., 1999), which is present at a high concentration within some of the subcortical nuclei, specifically the globus pallidus, substantia nigra and red nucleus (Hallgren and Sourander, 1958; Hill and Switzer, 1984; Riederer et al., 1989).
Additional iron accumulation, in the form of stable free radicals, has also been detected in the dopaminergic neurones of the substantia nigra in association with the pigment neuromelanin (Jellinger et al., 1992; Zecca et al., 1996; Shima et al., 1997). "
1. For "ferritin", see below:
"Ferritin is a ubiquitous intracellular protein that stores iron and releases it in a controlled fashion. The amount of ferritin stored reflects the amount of iron stored. The protein is produced by almost all living organisms, including algae, bacteria, higher plants, and animals. In humans, it acts as a buffer against iron deficiency and iron overload."
2. The color of ferritin was not specified. However, searching Google for "ferritin color" yields 2,400,000 claimed references.
Ferritin from equine spleen Type I, saline solution | Sigma-Aldrich
So, it's possible that at least some of the red nucleus' redness is due to ferritin. In order for this to be the case, ferritin's redness must fade when it dries and is exposed to air since the red nucleus is only red when it's "fresh". There's also the problem that it is present at a high concentration within some of the subcortical nuclei, specifically the globus pallidus, see above, yet the globus pallidus is pale rather than red.