In AC there they use the same chips for Poker as they do for other table games. The exception is in the case of denominations like $20 at Harrahs where the dealer will usually color you to white or red to keep them out of the game (just to make it a little easier for everyone).

A drop chip (not used in AC but used in LV, California, and even places like connecticut) are odd denomination chips ($2, $3, and $4) that are in the dealers tray used for dropping into the rake box. So while the game is going and the dealer is taking dollars for the rake, when it hits the max ($4 for example) they will change the 4 $1 chips they have collected from the pot for a $4 from the tray (placing the $1 in the tray and dropping the $4). This way the rake box does not get filled too fast (you'd guess a quarter the speed) and they don't need a fill on the table as quickly.

Binions (LV) uses a $4 chip for the drop chip and will sell them to you (if you ask - they ALWAYS say they are not supposed to but I've never been turned down). California card rooms use them quite frequently as do other areas.