3. Suppose you are viewing a sample from a PURE culture and observe both red and purple cocci. What are the possible problems that would cause such an inconclusive result?

The culture might not be stained properly or the culture might be too old.

Explanation:

Gram staining is done to differentiate between gram-positive and gram-negative bacteria according to the difference in their cell wall. In gram staining, the gram-positive bacteria appears violet and gram-negative bacteria appear pink in color.

Therefore if a pure culture contains have both red and purple cocci that it can be concluded that the gram stating was not done properly like too much destaining was done or too much safranin was used or maybe the culture is too old so that cell wall of some bacteria degrades.

not sure if this is what you'r looking for eubacteria and archaebacteria