MRampAttribute allows you to create an adjustable curve or color attribute where users can insert and adjust the interpolation of points along the ramp.

To create ramp attributes, we call the convenient classes contained in MRampAttribute:

MStatus RampAttributeDeformer::initialize() {
  // Create the curve ramp attribute
  aCurveRamp = MRampAttribute::createCurveRamp("curveRamp", "cur");
  attributeAffects(aCurveRamp, outputGeom);
  // Create the color ramp attribute
  aColorRamp = MRampAttribute::createColorRamp("colorRamp", "cor");
  attributeAffects(aColorRamp, outputGeom);
  return MS::kSuccess;

To access the ramp attribute values inside a node or deformer:

MStatus RampAttributeDeformer::deform(MDataBlock& data, 
                          MItGeometry& itGeo, 
                          const MMatrix &localToWorldMatrix, 
                          unsigned int geomIndex) {
  MStatus status;
  // Get the ramp attributes
  MObject oThis = thisMObject();
  MRampAttribute curveAttribute(oThis, aCurveRamp, &status);
  MRampAttribute colorAttribute(oThis, aColorRamp, &status);
  float rampPosition = 0.25f, curveRampValue;
  MColor color;
  // Get the corresponding value on the curve ramp attribute
  curveAttribute.getValueAtPosition(rampPosition, curveRampValue, &status);
  // Get the corresponding value on the color ramp attribute
  colorAttribute.getColorAtPosition(rampPosition, color, &status);
  // Do your calculation with the values
  return MS::kSuccess;

You will also need to make sure the attribute is set correctly in your attribute editor template for the node:

global proc AErampDeformerTemplate( string $nodeName )
    editorTemplate -beginScrollLayout;
        editorTemplate -beginLayout "Ramp Deformer Attributes" -collapse 0;
            AEaddRampControl( $nodeName + ".curveRamp" );
            AEaddRampControl( $nodeName + ".colorRamp" );
        editorTemplate -endLayout;
    editorTemplate -addExtraControls;
    editorTemplate -endScrollLayout;
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