I'm leaning towards an Evil Sunz themed army and my paint scheme reflects this, i.e. quite a bit of red, but much of it is equally applicable to all Ork clans.
The recipe, starting from a black undercoat (GW Chaos Black), is as follows:
I began by drybrushing various metallic items (weapons, armour, etc) in GW Leadbelcher, GW Warplock Brass and GW Gehenna's Gold (use this last paint sparingly). Do this first as it can be a little messy, then tidy up with black. Be sure to leave some of the plates and glyphs in black as these can be painted later in clan colours.
- Ork flesh - Foundry Dragoon Green shade
- Trousers/Vest/Boots/Straps/Pouches - a variety of browns or leave some bits black. Good browns are GW Mournfang Brown, GW Scorched Brown, VMC Leather Brown, Foundry Spearshaft shade, VMC Flat Earth - just get a good mix of dark/mid/light browns.
- Tip - paint any bits you definitely intend to remain black in a coat of black paint - I found that the GW Agrax Earthshade dissolved a little of the spray undercoat and turned some parts of the model cloudy! A quick re-paint solved the problem but it's best avoided in the first place.
- Armour, plates, glyphs, etc that are going to be red are first given a layer of a good red-brown, e.g. Foundry Conker Brown shade. It covers the black easily and is a good base for the 'proper' reds. Follow with a couple of coats of GW Mephiston Red.
- Any details that you'd like in yellow should now be painted in a light brown or ochre colour. If your contrasting colour is different then just pick a slightly darker shade as a base.
This is nice and easy. Wash with GW Agrax Earthshade being careful to avoid any unsightly pooling of the wash then set aside to dry thoroughly.
Metals - highlight (drybrush very carefully) with the base colours but leave plenty of the grimy, washed base colour showing. Be sure to pick out any sharp edges. The GW Warplock Brass can look good with a very faint highlight of GW Gehenna's Gold but go easy!
Flesh - here I used the full Foundry Dragoon Green triad as I felt that getting the Ork skin right was key to the overall look of the figure.
Red - GW Mephiston Red then a few highlights of GW Wazdakka Red, again pick out any edges.
Yellow - I've used Foundry Ochre light (as it's the only yellow I have!)
Trousers/Vest/Boots/Straps/Pouches - highlight the base colour and maybe add a few very quick highlights of a very light brown (compared to the base) for some extra depth. Black can be highlighted with a very dark grey or charcoal colour such as Foundry Charcoal Black (34B).
Add a few dags or checks here and there. Do this in yellow or black & white. Glyph plates look good in colours that contrast the surrounding area, e.g. a gold or yellow glyph on a red background. Pick out the teeth and claws with Foundry Boneyard shade & mid and the eyes with GW Mephiston Red. These figures have lots of extra bits and pieces so take a few moments to pick them out.
I've opted for a desert theme as I think this will look cool and fit in nicely with all the desert style terrain I've built in the last year or so. It's the same recipe as I used on my DAK. A base of Americana Country Maple followed by highlights of Americana Tan, VMC Dark Sand and Foundry Boneyard light. Then add a bit of clump foliage and a some tufts.