Final answer:
The iodine test for starch cannot be performed on very dark solids or liquids that do not permit the observation of a color change.
Step-by-step explanation:
The statement is true. The iodine test for starch cannot be performed on very dark solids or liquids that do not permit the observation of a color change. This is because the iodine test relies on the formation of a deep blue color when iodine reacts with starch. If the sample is already very dark in color, it would be difficult to observe this color change, making the test ineffective.