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Ok fellas i've tried several times to try and get this colour but it seems to fail every time. Its not actualy for a nightbringer model i jus love the colouring in the model. Google Image Result for http://www.gosfordhobbies.com.au/shop/images/P/newimagelge-67.gif
That look like white over light grey. I can't tell if there is some blue in there. I think you can do that by painting it all white and then shading it with light grey and then a little grey that is slightly darker but still light. Or you can paint it grey and work your way up to white. I think it just takes time to do it that way.
I got a similar result on my OK Gorger by starting with white, a couple washes of spacewolf grey then building it back up to white. I'll see what I can do about getting a photo
Id say it was done on a space wolves frey base and highlighted till almost skul white, alternatively you could start with a skull white basecoat and just carefully shade with Space wolves grey and shadow grey.
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After looking at the model Its not quite the same effect (its been a long time since I half painted him). I think it was either a Horizon blue or ice blue wash. I got Horizon blue in a late '80s to early '90s citidal paint set (Imperial Armour I think) so the name is probably different now if they still even make it.
You could add codex grey to the above blues and wash that over white then build it back up or just use SW Grey which i use for a base colour whenever I paint whites.
i'm pretty certain there was a White Dwarf tutorial on painting that Nightbringer. the 'Eavy Metal team 's method includes lots and lots of watered down layers, almost of wash quality, to ensure smooth transitions. if i remember, the skin used blues and the cloak grays and black.