Uma,
I am experiencing the same issue as Gintautas when adding a UniqueValueColorizer to a new raster layer. I am developing on ArcGIS Pro 2.4.2. If I use the VALUE field for the unique values, Pro changes the field name in the TOC to the only text field on the attribute table (NAME) and cannot display the layer. Image of incorrect TOC: 
If I use the NAME field for the unique values, everything works fine. The code you provided to initialize the colorizer results in the color ramp that I am expecting.
It seems that this may have something to do with using the LayerFactory to create the raster layer shortly before symbolizing it. I also tried getting the layer from the map instead of directly from the LayerFactory but this did not change my results. Let me know if I can provide any additional information to help with troubleshooting.
Also, for anyone migrating code from ArcObjects, I found that some of the color ramps that were formerly found in the "Default Ramps" style category can be found in the "ArcGIS Colors" style category in Pro. I am working with the "Elevation #2" color ramp.
Like Uma mentioned above the CreateColorizer method appears to have some issues. I looked at the colorizer result and the values[0] property in the group / classes appears to have the wrong value. I wrote a workaround to 'hand-correct' those values (i also overwrite the label - but that's extra) by using the raster's attribute table to look up the correct values - needless to say you have to adapt this code to use your raster fields:
protected async override void OnClick()
{
var raster = MapView.Active.Map.GetLayersAsFlattenedList().OfType<RasterLayer>().FirstOrDefault();
if (raster == null)
return;
await QueuedTask.Run(() =>
{
string fieldName = "ericlookup"; // Landuse or value or ericLookup
var style = Project.Current.GetItems<StyleProjectItem>().First(s => s.Name == "ArcGIS Colors");
var ramps = style.SearchColorRamps("Green Blues");
var colorizerDef = new UniqueValueColorizerDefinition(fieldName, ramps[0].ColorRamp);
var colorizer = raster.CreateColorizer(colorizerDef);
// fix up colorizer ... turns out the values are wrong ... the landuse value is always inserted
// we use the Raster's attribute table to collect a dictionary with the correct replacement values
Dictionary<string, Tuple<string, string>> landuseToFieldValue = new Dictionary<string, Tuple<string, string>>(); ;
if (colorizer is CIMRasterUniqueValueColorizer uvrColorizer)
{
var rasterTbl = raster.GetRaster().GetAttributeTable();
var cursor = rasterTbl.Search();
while (cursor.MoveNext())
{
var row = cursor.Current;
var correctVal = row[fieldName].ToString();
var correctCnt = row["count_"].ToString();
var key = row[uvrColorizer.Groups[0].Heading].ToString();
landuseToFieldValue.Add(key, new Tuple<string, string>(correctVal, correctCnt));
}
uvrColorizer.Groups[0].Heading = fieldName;
for (var idxGrp = 0; idxGrp < uvrColorizer.Groups[0].Classes.Length; idxGrp++)
{
var grpClass = uvrColorizer.Groups[0].Classes[idxGrp];
var oldValue = grpClass.Values[0];
var correctValue = landuseToFieldValue[oldValue];
grpClass.Values[0] = correctValue.Item1;
grpClass.Label = $@"{correctValue.Item1} ({correctValue.Item2})";
}
}
raster.SetColorizer(colorizer);
});
}
With the workaround i was able to code against any of the fields in the raster's attribute table:
Here is the default symbology after i added the raster to my map:
and here are some tests using different field names:
