H's result was one dead flower ... not surprising ... stuck in a dark room = no photosynthesis = no growth = death.
H loses is "control" part of his "experiment".
Q gives no idea the colour of H's flowers in expt.
H "shows" that a watered plant in sunlight with a bit of fetilizer tends to grow. He could have had a look outside at a garden to see that.
improvement by not killing the "control" plant. put it side by side with the test plant, so both get the photo stuff. Then measured fertilizer in test plant, and same water minus fert in control.
As for the colour I've no idea.