One of the negative issues that arise when you're an IV drug user is how imprudent and difficult it becomes to openly ask those around us questions when we have injection-related health problems. Thankfully there are forums such as this that can point us in the right direction. I'm not convinced, however, that the answers provided so far are all that helpful in this case (except for the one given by Cyc).
Now, you didn't say much about the size and over-all appearance of the discoloration. Track marks are "...a series of dark scars that follow the veins in individuals who chronically inject..." This was the most accurate and concise definition I could find at the moment (from some site call The Free Medical Dictionary by Farlex). So, if the purple discoloration is indeed confined to the line of your veins, you just very well may have track marks. Yay, right?
But if it looks splotchy and has no direct connection to the veins, what Cyc had to say is probably worth looking into. When we injure (this definitely includes injecting) our feet, they take longer to heal because gravity impedes circulation (this is true of all healthy and unhealthy humans alike). But if we then add on a disease or condition which further fucks our circulation, our feet are likely to show the signs first.
As IV drug enjoyers, we really do put our kidneys at risk. More so if we shoot up pills. So, if I were you, I would pick an arm to stop shooting into and allow it to heal a bit, then go to the doctor and ask to have some blood tests done (like to CBC, chem 20, etc.)... okay, so it may be odd or even suspect to just ask for those tests. So if you'd rather not share your drug use with this doctor (it's your choice), one condition that will always lead to these tests is complaining of kidney/bladder problems.
Hope this helps get you headed in the right direction. And don't believe everything you read on here; always verify info independently for your own sake. %)
