Hello Elmar,
The following script example shows how to select the tie points according to the RGB color values and tolerance:
import Metashape, sys
doc = Metashape.app.document
chunk = doc.chunk #active chunk
point_cloud = chunk.point_cloud
points = point_cloud.points
tracks = point_cloud.tracks
r = 217 #int(sys.argv[1])
g = 175 #int(sys.argv[2])
b = 164 #int(sys.argv[3])
tolerance = 10 #int(sys.argv[4])
for point in points:
color = tracks[point.track_id].color
if ((abs(color[0] - r) < tolerance) or (abs(color[1] - g) < tolerance) or (abs(color[2] - b) < tolerance)):
point.selected = True
Metashape.app.update()
print("Selected.\n")