Getting healed tracks covered to the point where a Dr won't notice them IS possible, but it takes a lot of work and the right equiptment.
The first thing you need is a palette of concealers specifically for covering tattoo's and/or bruises/scars. Ebay will have what you need. You want the product to be kind of waxy, with no shimmer. Then you need to learn how to use it. First, exfoliate, dry and moisturise the area. You may wish to shave your arms for a smoother working surface. Working with the same colour wheel that is used by make-up artists generally, 'opposite' colours are used to neutralise scar colors. Yellow correctors cover purple marks, peach covers blue, purple/lavender covers yellow, green covers red, pink/red covers green. Google color correcting make-up for more details. After colour correcting layers have been applied, a concealer which matches your skin shade exactly is applied over the top of these neutralising colours. Both for neutralising colours, and the skin shade, very light, thin layers of concealer are built up gradually, patting them onto the area. Everything needs to also be blended into the surrounding skin - the skin-shade concealer should spread beyond the track mark area. More than one colour is usually required, as is precision - cotton buds may be needed to apply exactly the right colours to the right spots. If you've used waxy concealers, you shouldn't need a powder product. If you did not shave your arm, you will need to remove concealer from the hair, or it will look obvious. Wrap tissue paper around a pencil and using your thumb to apply pressure, roll/pinch the pencil up the length of the hair - concealer should be deposited on the tissue.
A considerably easier way is a temporary tattoo - just make sure its dark enough, and ideally contains a lot of the colours of the tracks, rather than being just black.
