A lot will depend on exactly what kind of paint it is (the orange stuff). If it's some kind of latex house paint, there probably isn't much you can do apart from trying to peel/scrape it off. If it's some kind of oil-based house paint, or some kind of synthetic enamel-type paint, you MAY be able to remove it by soaking a cotton rag with paint thinner, wrapping the rag around the frame and allowing the thinner to soften the orange paint. You'll need lots of rags, and lots of thinner. If the orange paint does soften, use another saturated rag to gently wipe off the orange paint. If paint thinner doesn't seem to work, try acetone. Make sure you wear gloves and a mask.
The theory here is that the orange paint will be newer and softer than the harder, original professional paint underneath, and thus will seperate off the original paint.
This will be a big and messy job! It will be pretty difficult to clean the orange paint completely from all the little nooks and crannies like around the seatstay and chainstay bridges, lugs, braze-ons, and such. And ultimately, you could well damage the original paint that you're trying to save (and it may be in sad shape anyway).
But....nothing ventured, nothing gained; give it a try on a toptube/downtube/seat tube and see if it works. Decide how to proceed from there. Good luck!
~Sherry.
All vintage, all the time.
Falcon Black Diamond
Gitane Tour de France
Kuwahara Sierra Grande MTB
Bianchi Super Grizzly MTB