It is shown that when a god-enhanced Super Saiyan's power surpasses the power of the Super Saiyan God form, it will naturally progress into a Super Saiyan God Super Saiyan. "when Goku's god-enhanced Super Saiyan form evolved into Super Saiyan Blue, it also caused him to re-acquire his non-god-enhanced Super Saiyan form." So this is what is confusing about it, it claims that once SSGSS is acquired the other SS forms are reacquired
Why is it that every fan, when combing SSGSS and SSj4 (or even more confusingly, SSG and SSj4) has them with blue fur and hair? Blue is the result of yellow and magenta. How would Blue and Black or red make blue again?
Also, the original concept idea was that only the eyebrows and head hair would change colors to ssj, so why do people think that the body fur would change too?
Blue is a primary color, you can't combine it with another color to make it. As for the question I don't know the answer. And Goku didn't lose his other Super Saiyan forms.
Yeah. But yellow and magenta don’t make blue
Super Saiyan Red turned his hair red from black then blue when introduced to gold, so maybe it’d turn his head hair in SS4 red and his body fur gold/a more vidrant red.