An interesting thing happened some weeks ago, when I switched from oral to sublingual estradiol, thus significantly increasing my estradiol level. The skin on the underside of my... penis... (pre-op mtf) just where the urethra is hidden (or "raphe" line) got much darker than before, much more pigmented. It's about half inch wide and goes all the length.
Well, in natal female genitals, labia minora tend to get and stay dark either during puberty or during pregnancy, apparently because of heightened sex hormone levels. So it's not suprising the "male" genital skin could darken on estradiol as well... but...
But the most interesting part is that when one looks on a diagram showing the homologues (developmentally coresponding parts) of the female and male genitalia (such as this one:
https://bedahunmuh.files.wordpress.com/2010/05/homologues-of-external-genitalia.jpg , NSFW! ), one can see that the very part of the penile skin that got dark in my case is what was supposed to be the labia minora skin! (red in the linked picture)
So I can say that I reached puberty and my labia minora got dark

If only they were sitting in a place where they were supposed to be... sigh...