The darker brown the base the higher the value, your OP is a lighter colored "Chocolate Cow" the base can vary quite a bit as long as it's brown w/o a red cast. Maybe Sami @machinemades will chime in on the subject ?? I sold mine a few years back for $400.00 and it had a super dark brown base. David's OP is a Chocolate cow, @ least on my monitor it shows as a brown base w/o a red cast. There are some dark & light ones for you to take a look @ on this link.
LINK :: https://www.allaboutmarbles.com/viewtopic.php?f=7&t=45829&p=335789&hilit=peltier+chocolate+cow#p335789