I'm going to throw my inexperienced eyes into the foray and say you have a G. rosea. The photos I found of G. sp concepcion scopula leads me to believe what you have here isn't one (their leg segments seemingly have a lot more setae in between them on the underside). Then again, I could be completely wrong so...-.-
As to color forms from what I know G. rosea itself is what was once G. rosea RCF (when G. porteri was still being sold/misclassified as G. rosea).
Right. i was pretty sure that i could rule out the concepcion for the reason you mentioned but even recently i have heard that there is a Normal color form and red color form of rosea. ai will try to find the other post to check myself...
There is no RCF or any color forms....this drivel comes from decades of misidentification....each "percieved" color form is actually their own seperate species....in years past this would have been RCF, today we know its rosea....the true rosea.
The other "color forms" are either porteri, sp. north or concepcion.....different species, not actual color forms. Years ago all these species were [incorrectly] grouped as rosea and all simply called rose hairs, hence the confusion and why everyone with a "rose hair" thinks they have rosea...when most actually do not.
The "dark" color form you posted just above, isn't a color form, its a porteri, a different species altogether (but still known as a rose hair)....more common names causing consistent confusion.