In Yellow, I’d recommend Diamine Amber or Pennonia Dungo, Maybe R.O. Yellow Sunset.
Orange…since Apricot is discontinued and (some think) replaced with Kin-Mokusei, do you feel that’s an adequate-enough dupe? Sailor USA Florida is pretty great too and Anderillium Flapjack Octopus Orange. I also love more red-orange variety, like Kobe Bauhaus and Pennonia Roka Koma.
Red’s are hard to decide but I really love F-C Urushi Red, not a perfect center red but I love it.
Purple/Violet, J. Herbin Violette Pensee is one I compare to other similar Violets as the point of departure. Waterman’s Tender Purple is pretty great too.
Blue: Diamine Presidential blue, it’s about as close that I can find to a center blue. But I love the more purple leaning blues like Sailor Nioi-Sumire or the (now discontinued) Sailor Ultramarine.
Teal is hard, most of the great teal inks are LEs (i.e. KWZ pen show inks and Diamines LE shop exclusives). But I do really enjoy Sailor USA California even though it’s little too much on the blue side, but more teal than Sailor Yama-Dori. Or one of the darker Sailor Ink Studios like 764.
Green: KWZ Green #5 and Pelikan Aventurine are great center greens, but my GOAT green is Teranishi Guitar Taisho Roman Hikara Gentle Green.
Brown: Sailor Tea Time Fika was one the best but was an LE. 3 Oysters Americano is pretty close.
Grey, Yes, Diamine Earl Grey is great. I love 3 Oysters Doldham too even though it’s kind of a “French Grey”. F-C Graphite 4b is really great too but maybe too dark to be called a true grey!
Black: J. Herbin Pearle Noir and PenBBS Mark Twain are really great!
PCB, fully agree!
Blue-Black, so few inks that people consider blue-black I would actually consider blue-black. F-C Noir et Bleu is really close but probably too grey-black leaning. To me Blue-Black is like a US Navy Peacoat blue-black or what some call a steel blue or suit navy blue. Sailor USA Pennsylvania is pretty close to me, Maybe Taccia Hokusai Ainezu.

This was fun!