[abenedik]

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Each ModelNode object (also BoxModelNode) has Material and BackMaterial properties. You can set different materials to those properties, and the object will have different front and back materials. For example:

Code:

var planeModelNode = new PlaneModelNode(centerPosition: new Vector3(0, 0, 0),
                                        size: new Vector2(200, 100),
                                        normal: new Vector3(0, 1, 0),
                                        heightDirection: new Vector3(0, 0, 1))
{
    Material = StandardMaterials.Blue,
    BackMaterial = StandardMaterials.Red,
};