Waxing cloth getting dirty

[Cartman]

I washed and dried my truck and it looked good but I started waxing it and the applicator cloth started to get brown, am I not washing well enough or is it normal to pick up some dirt/other containments as the wax is going on.
If it makes a difference it looked good after and I was using Mothers 3 step process.

 

[mattadams]

I think thats normal. Every time I wax mine, I do a good wash job before starting including using some "quick detailer" to get off any watermarks and the cloth still turns brown. I think there is just some residue that wax is good at cleaning that other stuff can't get off.
To do a really good job I've heard of using the clay bar you can find to get the vehicle REALLY clean before waxing (clay bar removes a lot of the old wax residue, etc.) Do a search on "clay bar" for more information on that though.