Over time, the original paint of a vehicle fades and oxidises. Barring extreme cases, this process is usually not noticeable unless there is a new coat of paint to compare it to, usually referred to as cut off lines, which contrast from the fresh coat against the faded original coat. This effect may be emphasised if your original coat of paint uses a clear top-coat and you did not apply a new top-coat to your working area. If your vehicle is of earlier make and model, it is possible that your vehicle does not have a clear top-coat at all, but rather just a very thick base coat.
To diminish (or completely remove) the contrasting effect, you will need to cut and polish the working area and the area surrounding it. Followed by a thorough clean with alcohol.
Masking: Mask out all areas you do not want to blend. Masking is a very important step especially when blending because you need to blend into areas that will not be totally masked.
Using 2000 grit sand paper, wet scuff beyond the area to be blended so you have a section to melt your clear coat to. You can use a paint blender that you mix with your clear on the last coat OR you can mix reducer - 10% clear/90% reducer and load your spray gun.
Apply your base colour in a feather spray pattern only covering the primed areas first. Gradually widen your coverage over two to three coats until your base coat starts to blend with the original base colour on your panels.
Clear coat Time: Clear all of your panels except the blending areas twice until you get that high gloss look all over except where you want to blend. On the last coat you will mix reducer with your clear. Mix the proper amount according to the packaging instructions and blend only over the section where the clear is dry looking.
Carefully blend the clear coat. (More like melting the clear with the reducer to the panel).
Buffing: Wet sand the entire paint blending area with 2000 grit paper and buff.
You can polish either by hand or by machine. Hand polishing can be time-consuming and can often lead to defects such as holograms on your working surface. DA (Dual Action) polishers are quite paint-safe and do not carry the risk of damaging the working surface or burning through it.
You will save thousands of dollars by doing it yourself, not to mention the money you can make by fixing friends and family’s cars in your spare time.