+1 on everything that has been said above.
There are only a handful of ways you will see 'color' transfer on the pad.
From cleaning the paint- Even after claying and washing a car (often an older 'beat' up car) you might get a little color transfer from dirt that has 'stained' the paint. Usually this color transfer will often be a different color then the car (unless the staining is happens to be the same color of the car of course).
Every year my grandmother stays with us for a couple of months and drives from Colorado to Florida. She lives in the mountains outside Colardo Springs, which have a lot of clay. Every year I detail her Blazer which is white. The first time I polished it (even after washing and claying it) I was getting orange transfer on the pad from the clay that had embedded into the paint.
From going over rubber trim and seals- This can pick up a black/dirt color on the pad.
From polishing a single stage paint or a paint that as a tinted clear coat (which I guess really isn't clear)- The color transfer in this case is a result of the paint itself mixing with the solvents in the polish and 'sticking' to the pad.
From striking through the clear coat on a clear coated paint- In this case the clear coat is removed and the polishing pad contacts the color coat underneath. As with polishing the single stage/tinted clear paints, the pad is stained by the color of the paint itself.
So how can you tell the difference between single stage/tinted clear coats and 'strike through'...
When you strike through a clear coated paint you will will noticed that the area that has been struck through will have a different tint (and often less sheen) then the surrounding areas. It will be noticeable when you wipe away the polish.
The you polish a single stage or tinted clear coat you should (provided you are using the right polish/pad) notice and improvement in the gloss and clarity but it will be gradual.
Keep in mind that many older cars that have been repainted at various times can have panels that are clear coated and panels that are single stage.
This is why we alway recommend using the least aggressive method of polishing first. Start with something gentle and do a test section.
If you notice color transfer with a mild combination you likely have single stage or tinted clear coat. If you happen to 'strike' through with the least aggressive method (which will be noticeable when you wipe off the residue) then it really isn't your fault. If the paint was SO thin that you could strike through with a finishing polish/pad, then the reality is that paint is days away from total failure.
I wouldn't be overly surprised if you notice some panels are single stage and some are bc/cc.