Had a thought on Bladeguard colors:

[Tacitus]

I'm thinking of painting some up in Deathwing Bone of course, but I'm also thinking of painting a set up in 30K Dark Angels black to represent the Fallen who flocked to the Lion (Since he was sold with some as a set) based on the head cannon that they joined the Lion and the Lion put them next in line to cross the Rubicon as his personal retinue. 

[m_r_parker]

As a suggestion, you could also lean into more of the 30k aspects if you're looking towards Astartes who were present in that timeframe. Keep them majority black armour, with specific armour plates re-coloured into bone to show where they've taken hits in place of their liege (e.g. the Lion). Best of both worlds option.

[Interrogator Stobz]

Agree with m_r_parker, black with bone and red parts.

 

Or paint them the same as your version of the Lion.

Edited August 16, 2023 by Interrogator Stobz