Well, we currently have the following: (I hope that I get this correct)

Yellow - Eldar

Red - Chaos Marines

Blue - Space Marines

Green - Orcs

Speculation:

Purple - Dark Eldar ?

Black - Necrons ?

White - ??? Tyranids

Brown - Astra Militarium ?

??? - ???

Thoughts???

Tau: light brown

Tyranids: bleached bone

Dark Eldar: purple

Necrons: grey

Astra Militarum: black

Necrons and Imperial Guard could be other way round, as grey feels right for Astra Militarum.

My guess

Tau: light brown

Tyranids: bleached bone

Dark Eldar: purple

Necrons: grey

Astra Militarum: black

Necrons and Imperial Guard could be other way round, as grey feels right for Astra Militarum.

My guess

These colors sound perfect. Possible switch between Necrons and Astra Militarum as you mentioned.

Astra Militarium? That didn't exist back when I played 40k back in ~2000...

Edit: Oooh, Imperial Guard! I'll show myself out, tyvm...

Astra Militarium? That didn't exist back when I played 40k back in ~2000...

Edit: Oooh, Imperial Guard! I'll show myself out, tyvm...

Don't give in to their IP-registering ways!!!! They'll always be Imperial Guard in my mind and I'll always refer to them as such!