I’ve seen the prayer bumps on heads, often darkish as well as raised. I wonder how long they take to develop.
Some of those 'prayer bumps' (many/most) are enhanced, shall we say. Usually to imply more piety than is earned. A technique I learned while living among them was to slice a zuchinni or similar, heat the sliced part on a skillet and apply to forehead. That evidently presents as a more reddish mark, more authentic. Another technique is with a hot rock, which usually presents as a more dark spot (or spots).