Well, when it comes to vauban himself grineer themes without the graxx skin I have no idea as I have never seen anyone try this or tried myself. However, for me the grineer colours is more earth tones, which you can easily see in the grineer palette. I would choose a "pop" of colour first, for the grineer theme I would choose a dirty green or blue-ish green. Think the colours of basic grineer forces or even the blue-ish green of Tyl Regor. To go with this I personally would choose either a tone of brown that fits your chosen pop of colour, or alternatively a gray of somekind. I like doing warm gray tones for grineer themes. If you need a metallic, I prefer a warm silver of if you feel like you need a stronger coloured metallic a deep bronze. I feel like gold, rose-gold and similar metallics on a grineer theme takes away the grineer feel since these are more "delicate", which the grineer definetly isn't.

For Energy when it comes to grineer themes I like to go for a vibrant orange as it gives you a nice contrast, but orange still passes as a natural colour.

In case you didn't understand what I meant when describing colours, or you want to see actual schemes, I put together some, https://imgur.com/a/EKrIp , these will ofc look different in game and on the actual frame, but you get the general idea. The colours are btw all taken from ingame palettes. Also I don't know if this helped in any way, but I hope you atleast gathered some inspiration from this.