"My apologies to you but the apologies, and any refunds necessary, should come from the promoter/s of this festival. We will still rock on ... All the best Sharon."
But Ms Colvin is downplaying the situation and said the second festival of its kind is on track for success, with "tickets flying out the door".
"Sharon [O'Neill] is not a massive loss," she said.
"There are a lot of rumours going round but please ignore them. It's not about money.
"We have changed the line-up, we've added a couple of reggae acts because we think they're a better fit for Northland."
That "fit" now includes The Narcs, reggae band Trible Conexions, blues band Kokomo, local singers Terina Kahle and first-time festival performer Kahuna Jack, and others.
Several of O'Neill's backing band, the All Stars, including Liam Ryan from The Narcs, are already in other bands performing on the day.
Anyone who bought tickets especially to see Australian-based O'Neill would be refunded, Ms Colvin said.
Ms Colvin said she had fully paid O'Neill and other dumped performers but O'Neill's New Zealand manager Aly Cook, from the alt-rock-country band Sou'Westers - also canned from the festival - said only part of their fee has been paid.
About 50 people have commented on Ms O'Neill's Facebook page about her being dumped at short notice.