Admin you can delete my post if you think its unnecessary.
OP, you might know some of the steps but I'm going to think that you don't know anything at all so I'll try explain it as detailed as possible.
TO DO THIS STEP THERE MUST BE A SECOND ACCOUNT OR ANOTHER PERSON (PS3) SO YOU GET YOUR CAR BACK.
Remember there is a chance that you can lose your save data and I'm not the one held responsible for your own action.
P.S Done this a thousand times.
1.First you go into your GT5 look on the left side corner of your screen and you should be able to see a square with a little red circle in it (That's the save button). Click it and a bar should pop out.
2.Find a USB doesn't matter how big it is, plug it in your PS3 and go to GAME> SAVED DATA UTILITY PS3 (PS3). In there you should see GT5 Saved data and GT5 back up data I'm telling you right now NEVER TOUCH THE BACKUP OR IT WILL RUIN YOUR SAVE DATA. Go and press triangle on GT5 Save Data(Not backup one) then press copy and save it to your usb, now you have a copy of your current game, stats etc...
3. Go back into GT5 select your car customize it whatever you want to do with it, then do the painting last (Don't have to but it reduce any confusions), after painting the car and customizing it go back to your garage select another car and find the car you just painted send it to your second account or another trustworthy person. I'd recommend to your second account because you can access it and you can leave it there as long as you like but with another person they can't send it to you everytime but you do get it right away if the person is online. Remember if your sending it to your second account you have to wait for another day because I believe it's one trade per console.
4. Go back to GAME>SAVED DATA UTILITY (PS3), delete the GT5 in your Saved data not in the one in the USB! then go to your USB scroll down to GT5 press triangle Copy and then TA DA back to normal (You just dupe your colours).
5. Last step go back in GT5 and check your colours see if it's still there, it should be!