Take a look if that could help you. I do it all with acrylic colours and when referring to the satin and glossy coats I mean the #522 (satin varnish) and the #519 (gloss varnish) from Vallejo, "varnish" not mediums.
Colours range really does not matter, you could use the colours you prefer, you can also render a dark (black, gray, red etc.) base colour with light spots and/or veins.
1) Coat the piece with the base colour (in this case a mix of offwhite and sand) and do not care about brushstrokes.
2) Use the most fine brush and thinned paint to draw some veins, not so much, just a few and clearly visible.
3) Coat the piece with the satin or gloss varnish.
4) While the above coat is still wet use a very thinned paint to draw some blurred spots near to the previous veins, mix and blur the paint with the still wet satin/gloss coat on the place, in other words put a drop of paint and rotate the brush to blur the spot.
5) Let all the above stuff set well and paint some more spots (on set, not wet surface) with very thinned paint. You may need to brush those spots over and over again until the colour raise up by magic, the paint must be really thinned, almost dirty water.
6) Coat once again the piece with the satin/gloss paint.
7) Paint some more veins/spots on the wet and when all is set apply a final coat.
Using pure gloss varnish may give to the piece an unreal look, so always mix it with a bit of satin or matt varnish.
