Nope i believe it too.
In kurama flash back he is shown with blond hair. If it was red then the shade would be much darker.
Also it was hinted gold and silver bros were related to him. So again light hair colour.
Only twist could be, he exerted his life force and his hair turned white, but highly unlikely.
Well or simply turned old, then we'r at square one
Yoda belonged to a race of creatures like Yaddle who have extremely long lives (like the Uzumakis) Gandalf belonged to the race of Ainur, of the order of Maia, created by Eru Illuvatar before the beginning of the universe. Lol