Dual/Multi Land AI Colour Selection Algorithm

For a while i was experimenting with dual lands for DOTP2013. At this moment the current implementation works well.
The implementation is very simple, it presents the user with an ability with a prompt for a colour selection, then it enables the corresponding mana ability.
For humans this works well. But the AI sometimes make bad choices, or do not use them at all.
My question for you guys is what algorithm should be used to make the AI's choice?, and when this algorithm should be applied?
The most simple algorithm should be to do a "chroma count" (the number of mana symbols in all permanentes) in the player's hand minus the number of basic lands in play producing that colour, and the smaller value is the one we generate mana for. Do the check at the end of every step while the land is no tapped.
Any ideas?
The implementation is very simple, it presents the user with an ability with a prompt for a colour selection, then it enables the corresponding mana ability.
For humans this works well. But the AI sometimes make bad choices, or do not use them at all.
My question for you guys is what algorithm should be used to make the AI's choice?, and when this algorithm should be applied?
The most simple algorithm should be to do a "chroma count" (the number of mana symbols in all permanentes) in the player's hand minus the number of basic lands in play producing that colour, and the smaller value is the one we generate mana for. Do the check at the end of every step while the land is no tapped.
Any ideas?