Interestingly, some of the planes at williamsburg that have only been used a few decades are already dark brown like that.
They stamp the year on the bed now because the toolmaker has run into people trying to sell him back planes that he made (that were probably stolen or taken by employees) as vintage.
Beech and birch were common in the US for planes (birch first). If you are going to buy quartered beech that's only been kiln dried and not had a few seasons to dry and then spring back (it'll always spring back less than the shrink), you'll be grinding some width off of the iron in a couple of years - just be ready for it (or progressively if you're using them)
It does take some luck to find well sawn unused beech a few years old, though, that doesn't have cracking or bug damage or spalt.
Old dense heart mahogany would've made a nice plane, though it would also dent easily. Not sure how it wears compared to beech, but unless you're making a living with them, that won't matter.