Absolutely, brown/gold is the first stage in the color progression. That will appear in AT or NT as the first stage.
Sorry, but the OP’s original 1968-D and the 1964-D MS68 both look natural to me. I have seen the 1964-D MS68 in hand and it is a gorgeous example. The 64-D (photograph linked above) came from the Richard Green collection then it was part of the Larry Shapiro’s Type set. When Mr. Shapiro sold off his type set, my dad helped broker the deal. One collector on the west coast ended up with Richard Greens business strike (all in PCGS plastic) 1965 MS67, 1966 MS68 and 1967 MS67 while another collector from the south east ended up with Mr. Green’s 64-D MS68 and the 1976-S MS69. We ended up with Mr. Green’s (again all PCGS labels) 1964 MS67, 1968-D MS67, 1969-D MS67 and the 1970-D MS67. As far as colors go, the 1964-D MS68 that Mr. Green had was the most handsome one out of the bunch.
Sure Caleb, seems PCGS agrees with you. I didn't want to turn this thread into a toning discussion, so i'll let stop commenting after this one. I purposely never said it wasn't natural toning. I really now have become cautious in terms of toning, as PCGS usually is. I have seen plenty of examples that I was shocked that didn't get graded. Anyway, it's a beautiful coin and I would like it in my collection, don't get me wrong on that.