When looking at pennies, mainly wheats and older lincolns there is the rd, bn, and blank designation. Is one prefered over others? What's prefered.
A lot of collectors collect circulated (i.e. "blank") Lincoln because they are more affordable. Most of your serious collectors with ample money collect coins that look closest to the original mint state - i.e. red. Several collectors look for the RB coins because they like the looks of those coins best. And those who look for colors commonly are graded RB. I do not know of anyone who collects only BN coins, but I will bet there are some out there. Personally, I like the wood grained coins. They are usually RB or BN. Translation, collect whatever coin YOU like and can afford.
Although copper coins can tone very nice shades of green, I do not believe either NGC or PCGS have a designation for green. It's red, red brown, and brown only. Coins with full red mint color bring a premium, especially as you move back into early copper. One thing to keep in mind, that mint red color on coins will naturally tone brown with time. The toning process can be slowed down with proper storage, but given enough time it will tone. One interesting aspect of early large cents and half cents, most of the red, or red brown coins available on the market today are hoard coins. Uncirculated early copper which was saved via more normal collecting channels are more likely to be brown in color.
