Simon went up and down and finally came to a stop at the ceiling, where he floated for a while until he turned green and became heavy enough to slowly fall back down to the floor.
There he could still be found for another two hours until he completely dissipated.
During this time he might have changed coulors to red and purple or not.
For such is the life and death of potion fumes.
Even for sentient ones that the potion of one Hermione Granger caused. A sixth year Gryffindor whose formidable brewing abilities where second to only the teacher's...