The thing to remember with camo is that its designed to obscure the shape of whataver its applied to. In the case of humans it breaks up the face and the head/shoulders and suchlike. For vehicles the idea is to break up the man-made hard lines and sillhouette. Just painting blobs in the middle of plates doesn't work. You need to have the disruptive pattern (the blobs) mixing it up over the corners and edges of armour pates and the vehicle. Best source is a reference book on armoured fighting vehicles, or just google for Tank camouflage.
here are a couple of my schemes that I'm quite pleased with and were based on real-world camo:
Tau urban/mountain
Guard woodland: