The tall striker was booed during the no-scoring draw with St Johnstone and cheered as he was replaced as the sole frontman by teenage defender David Stephens.
And today Riley, chairman of the Hibs Supporters Association, revealed he'd been angered so much by the reaction of some of his fellow fans, he felt the need to speak out, claiming their actions were also harming Nish's team-mates.
While accepting every fan's right to criticise, Riley insisted those who had taunted Nish had "gone too far" and were wrong to single out individuals for such public humiliation.
He said: "Colin is a Hibs man through and through and, I am led to believe, so are his whole family. It must have been a dream move when he came to Easter Road but now it seems to be turning into a nightmare.
"I've always believed that once a player wearing that green- and-white jersey crosses that line he should be supported and encouraged. Like any other player Colin doesn't go out there to deliberately play poorly, he gives of his best in every match.
"If things aren't working out for him, or any other player, we should be supporting them not booing them. There is a saying in football that players win and lose as a team so it isn't right to single out any individual during a match.
"It's not only that particular player who suffers but the team as a whole as the other players hear what is going on and don't like it either.
"I know some may have a go at me for speaking my mind, but I have to say I was sickened to hear fans boo Colin while he was on the park and then cheer him when he was substituted.
"It was a hard, hard job he'd been asked to do and given the fact he was the only fit striker we had out of the 18 who stripped for the game if it wasn't him then who was it going to be?"
And Riley believes Nish's worth to the team is grossly under-estimated by some, pointing out the striker is in the SPL's all-time top ten list of scorers and reminding them it was his five goals in the final two games of last season which helped Hibs clinch fourth place and Europa League football.
Pointing out how both Ian Murray and Edwin de Graaf had jumped to their team-mate's defence, he said: "Colin gets on very well with the other players, Derek Riordan says it is great to play up front with him.
"Okay, Colin might not be your 30-goals-a-season man but he's proved over the years he not only gets his share but make them for others."