Yep, you're missing something.
You cannot process resources of the next higher tier until you finish the red portion of the lower tier and move into the yellow. For instance, you cannot prospect Barrow-Iron/Silver (Journeyman) until you have prospected enough Copper/Tin (Apprentice) to completely fill the first red tier of Apprentice prospecting and start the second yellow bar. This point also grants you a title as a prospector.
The second restriction is that you cannot start the yellow section of any tier until you fully master the tier below. So, you cannot start the yellow section of Journeyman (and thus not start Expert at all) until you complete the yellow section of Apprentice.
I know, I said I quit, so why am I posting? 'Cause there ain't no Blogorette patch.