Oh Gap. I also have issues with their sizing, so you are not alone!
You definitely don't seem invested in this blazer, so I'd agree with some of the other posters and you yourself and say keep looking!
I'm in Canada too, so maybe I can give you a bit of help with some colourful blazers I've seen around! I don't know where exactly you are, so I don't know if you have access to all these stores, but I hope you do!
Jacob has some really beautiful hot pink and royal blue knit blazers if you're interested in those colours.
OK, so Forever 21 is going to be way more hit and miss than even Gap, and the quality's not there, but seriously, last time I went in they had every single colour blazer imaginable, and they're all in one area (in my local one, all right at the entrance!) so you don't need to rummage around in the store. xD
As Aida mentioned, Zara's got some colourful blazers in stock now too. I don't know what colours they've got though!
I'll see if I can find some more options for you! (Canadian solidarity, yeah!)
EDIT: Le Chateau sometimes has coloured blazers. I don't generally shop there anymore due to personal reasons, but i have definitely seen red and blue blazers, and I do recall seeing more varied colours recently.