The response to light color does not stand on its own. That is merely one parallel from many. It is true plants do not have a nervous system like animals, but they do have similar responses to stimuli. Parallels can be drawn to sight, sound/touch and smell/taste.
Sentience is another topic that is defined subjectively. From context it is clear you make a central nervous system a foundational requirement. I could also apply this to technology, so I would need clarification from you to understand what it means to you. I do not hold to a personal definition for sentience because I have found neither a universal nor scientific understanding of the idea.
The response to light color does not stand on its own. That is merely one parallel from many. It is true plants do not have a nervous system like animals, but they do have similar responses to stimuli. Parallels can be drawn to sight, sound/touch and smell/taste.
Sentience is another topic that is defined subjectively. From context it is clear you make a central nervous system a foundational requirement. I could also apply this to technology, so I would need clarification from you to understand what it means to you. I do not hold to a personal definition for sentience because I have found neither a universal nor scientific understanding of the idea.
As for the last paragraph: yup.