Question on brain dissection

I was dissecting a sheep's brain for my students and one of them asked a question about the corpora quadrigemina he asked why did two of them(the superior colliculus) look more red than the other two and I have no idea why was that. also I read several topics about it but in the photos there was no such thing as I saw. can you help me with that?can it be due to any wrong doing in dissection procced? any help is appericiated

Watch the video: Πώς μπορούμε να αναπτύξουμε νέους νευρώνες στον εγκέφαλο. TED (January 2022).