Welcome to HCM
We understand your concerns
I went through your description. I suggest you not to worry. The method of masturbation
you mention here is the most commonly used method. Very few women use dildos or stimulator for masturbation.
The color change is due to over use of the portion and is also common. Your masturbation habit is, as you say, more and therefore more brownish the color. Nothing to worry.
Hope this clears your doubts. Available for further clarifications.