The ICE attribute shaders allow you to access ICE attributes that are driven by ICE trees. You can also apply the Attribute shaders to geometry that is used as shape instances on ICE particles.
These shaders allow you to control your shading based on calculations done by an ICE tree, thus creating a link between data in the ICE tree and data in the render tree. To use the attribute shaders, you must first make sure that the object or its components have the appropriate attribute created for it in an ICE tree.
For example, you can control the particle's transparency based on the distance to a surface by writing an ICE tree that sets a DistancetoSurface attribute and then accessing that attribute in the render tree via an attribute shader. Or make smoke dissipate or a color change with a gradient depending on the velocity of the particle.
If the shaders are applied to an object with an ICE tree, only ICE attributes from that object will be shown in the shader's Attribute drop down list.
If they are applied to an object that does not have an ICE tree, then all attributes from all ICE trees in the scene are displayed in the Attribute list for that shader. This is so that instances can choose attributes even if there is no bi-directional link between the Instance Shape node (or the Set Instance Geometry compound) in the ICE tree and the instance object itself.
There is one attribute shader per data type:
For an example of using this shader, see Using the ICE Particle Color in the Render Tree.
Quaternion (as rotation), Matrix 3x3, Matrix 4x4, and Rotation data — use the Transform Attribute shader.
2D vector, 3D vector, and Rotation data — use the Vector Attribute shader.
For information on each of the Attribute shader parameters, see Data > Attribute.
Open a render tree and click the Update icon or press F6 to display the render tree for the selected object.
In the render tree, drag an appropriate Attribute shader from the Data > Attribute group in the preset manager on the left, or choose a shader from Nodes 
Data Attribute on the toolbar.
Plug it into any input port on a shader that supports that data type.
For example, you can plug many of the Attribute shaders as inputs into the Particle Gradient shader to drive the color gradient based on almost any ICE attribute for the particles, such as their velocity, size, orientation, mass, point position, etc.
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