To create a new material layer, select an object, go to the Material panel in the Right Sidebar, then press "+" to add a new layer.
On Spline, materials work in a layer-based approach, which means that you can control an object's look by creating or editing layers on a vertical stack. This approach is different from traditional 3d editors, but it is akin to how most graphic design tools work.
The default material layers
By default, any object on Spline includes two material layers: Color and Lighting.
For 2D objects like the Rectangle and the Circle, the Lighting layer is set to "None", which means that it doesn't have any visual effect on the object. For 3D objects, the Lighting layer is set to “Phong” by default.
Layer Properties
All material layers are different, but they all share the Opacity and Blending parameters.