{Ultimate Price} and {Mutavault}
Does Ult. Price kill Mutavault?
No, {mutavault} is colorless since it is a land. Monocolored has to be colored.
105.2a (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=105.2a): A monocolored object is exactly one of the five colors.