Do you mean that enabling pdf-a in V3 would solve the color problem?
No. It just removes some transparency things to make the output compatible with pdf archive standard. So that won't help
I discovered the problem on our old production server with jsreport 2.11.
I see, v2 doesn't do anything with the colors. It's the output from chrome. I've never noticed this problem. Try to isolate the problem. Put just the image to a template, does it produce bad output? Try it locally. The same?
You can do whatever you want in the beforeRender. Like login to azure blob storage, download required images, convert to the base64 form and provide it to the req.data so template can set image src through handlebars.