Cumaru boards turning almost black after oiling — normal?

Applied DeckWise Ipe Oil (Hardwood formula) to a freshly installed Cumaru deck and some of the boards went nearly black. Others turned a beautiful warm brown as expected. Same product, same application method, same day. The dark boards don't have any visible defects — they're just absorbing the oil differently.

Is this a density variation issue? Will it even out over time? Client is concerned about the uneven color.