You can activate whether or not you want to use Absorbtion keys to open doors (much like with a Master Key), if you open a door using Absorbtion keys, you get <The Color of door you opened x amount of keys you used>, here is an example:

Absorbtion keys x4, Orange keys x0, Orange door with cost 3 opened with absorbtion keys

Result: Absorbtion keys x1, Orange keys x3

well, bicolor doors would probably grant the cost color keys. I don't know what a black or combo door does yet.

and i almost forgot: blank, master and pure doors cannot be opened by an absorbtion key.