Final answer:
Without additional context, it is not possible to accurately answer how Randy distinguished between red and yellow tulips. However, referencing Mendel's work, characteristics such as flower color or seed texture could be considered, with yellow seeds expected in a cross with green and yellow seed color where yellow is dominant.
Step-by-step explanation:
The question at hand does not provide enough context to accurately determine how Randy distinguished the red tulip from the yellow tulip. However, if this question pertains to one of the seven characteristics that Gregor Mendel observed in pea plants, we can refer to a related concept from Mendel's experiments which includes characteristics such as flower color or seed texture. As for a cross involving true-breeding parents with green seeds and yellow seeds, where yellow seed color is dominant, we would expect the F₁ offspring to have yellow seeds. When considering petunia flowers, the crossing of blue and red to create violet offspring might suggest incomplete dominance as the pattern of inheritance.