Could you elaborate on this so I can under this statement better? Painting one panel at a time? As in today you're gonna paint the hood, tomorrow you're gonna paint both fenders, the next day and so on? Not a good idea. Just to let you know that sometimes temp, humidity, reduction amounts, hardener amounts, variations in undercoat colors, can cause a color change in the top coat. True it will be by a small amount, but once all the panels are bolted to the car, that small amount can be very noticable side by side.