The first models I painted getting back into the hobby were painted as White Scars. This ended up being a kind of Khaki. One major reason I chose to repaint them as Ultramarines was blue. There is a fantastic series of blog posts on color theory applied to painting miniatures from theback40k blog. The first (of three) can be found here.
After reading that blog I realised why otherwise well painted miniatures often looked odd or busy was due to the use of opposite colors. A more analogous scheme would look more, not real, but something like it. Perhaps believable would be the word. I thought blue armor with green squad markings and green/yellow helmet lenses would work. Red purity seals would provide a bit of contrast.
Some time ago, for an unrelated professional development project, I learned to use Adobe Creative Cloud. Mainly InDesign, Illustrator and Photoshop. The back40k articles really helped me make the link between graphic design and miniature painting. A really useful tool for sketching out color schemes is Paletton. It’s a free online tool intended for creating color schemes for websites. It can be found here.
As for the Sauroters color scheme, I’m really not sure yet. I want to paint orange and I want to include visual influences from Ancient Greek pottery. In paticular I like the flat design of black, white and the color of the pottery. Orange is too bright for my tastes but something more desaturated would be good. Paint consistency is also important to me so I am looking at the Vallejo range for inspiration.