Bug: Dead man's chest won't let me pay with any kind of mana

[peepser]

I enchanted Chronoza (blue 3/3) with dead man's chest. It died. three cards went to exile. I tried to cast Krovikian mist from exile (power and toughness equal to illusions in play). It would say 'Pay mana cost 2'. But when I tried to pay for it using my black mana (using auto), it then asked me to pay '1B' mana. I could not cast any of the blues creatures from exile as they all required blue mana.

Am I misunderstanding 'dead man's chest'? I thought it meant I could cast any card from opponent's exile and my mana could be mana of any color.