public double MaximumValue {get;}

//var voxelLayer = ... ;
//Must be on the QueuedTask.Run()

//Get the variable profile on which to access the data
var variable = voxelLayer.SelectedVariableProfile;
//or use ...voxelLayer.GetVariableProfiles()

//Data range
//At 2.x - 
//var min = variable.GetVariableStatistics().MinimumValue;
//var max = variable.GetVariableStatistics().MaximumValue;

var min = variable.Statistics.MinimumValue;
var max = variable.Statistics.MaximumValue;

//Color range (Continuous only)
double color_min, color_max;
if (variable.DataType == VoxelVariableDataType.Continuous)
{
    var renderer = variable.Renderer as CIMVoxelStretchRenderer;
    color_min = renderer.ColorRangeMin;
    color_max = renderer.ColorRangeMax;
}

//Typically, the default color range covers the most
//commonly occuring voxel values. Usually, the data
//range is much broader than the color range

//Get the variable profile whose renderer will be changed
var variable = voxelLayer.SelectedVariableProfile;

//Check DataType
if (variable.DataType != VoxelVariableDataType.Continuous)
    return;//must be continuous to have a Stretch Renderer...

var renderer = variable.Renderer as CIMVoxelStretchRenderer;
var color_min = renderer.ColorRangeMin;
var color_max = renderer.ColorRangeMax;
//increase range by 10% of the current difference
var dif = (color_max - color_min) * 0.05;
color_min -= dif;
color_max += dif;

//make sure we do not exceed data range
//At 2.x - 
//if (color_min < variable.GetVariableStatistics().MinimumValue)
//    color_min = variable.GetVariableStatistics().MinimumValue;
//if (color_max > variable.GetVariableStatistics().MaximumValue)
//    color_max = variable.GetVariableStatistics().MaximumValue;

if (color_min < variable.Statistics.MinimumValue)
    color_min = variable.Statistics.MinimumValue;
if (color_max > variable.Statistics.MaximumValue)
    color_max = variable.Statistics.MaximumValue;

//variable.Statistics.MinimumValue
renderer.ColorRangeMin = color_min;
renderer.ColorRangeMax = color_max;

//apply changes
variable.SetRenderer(renderer);