Seems to me that W1 had variances, and also changed through the years:
My '68 Road Runner was a fairly warm color, had a little ochre & black in it.
My '69 Road Runner was markedly brighter, but not as blue in cast as most GM whites.
My '72 Duster was even warmer, more tan than the '68 RR.

It could also be that the white pick-up parts were painted by a vendor or multiple vendors.
To be accurate, you need to color-match your originals, obviously.