Aquic Subgroup Criteria

For an aquic argiudoll, the requirements in taxonomy state:
""Within 75cm of the mineral soil surface, in one or more horizons with a total thickness of 15cm or more that have one or more of the following:""

My question is: does the 15cm layer that meets the color requirments in sections a,b, or c, have to occur entirely within 75cm or does it just need to start within the 75cm depth?