# Getting color from a face/polygon via python to select the corresponding face/polygon

Okay, I need help again.

I've got a model with colored vertices. So far, there are only two colors applyed (red and white. It's a reference model which I use to define the script for automation). I need to select all white polygons in that model, so I can select them and hand the selection over to another function which generates another model based on the selection. Selecting the vertices is posing a problem, as vertices can have more than one color at once. So I tried to use the polygons.

Now, these polygons should have a color, right? How do I extract the color values so I can do something like this ((very) pseudo code):

for polygon in mesh.polygons:
if polygon.color == red:
plygon.selected = True


I read through other questions, but they all want to apply another color to a polygon. I don't need that. The color is already there. And it seems I have dive more into python to extract the snippets which would do the trick for me from the other answers.

• faces have a material poly.material_index. The material has a color. For vertex color see blender.stackexchange.com/questions/121933/… Jan 12, 2021 at 15:17
• how do I access the material? The importet ply gives me an empty material collection Jan 13, 2021 at 7:38

Welp, I don't really like to answer my own questions. But I found the solution and I wanted to share it with you :)

bm = bmesh.new()                          #Generate new bmesh object
bm.from_mesh(obj.data)                    #Assign the model mesh
for face in bm.faces:                 #goes through the faces
for loop in face.loops:           #goes through the loops of each face
if loop[bm.loops.layers.color[0]] == Vector((1,1,1,1)): #the left side is the vertex color
loop.vert.select = True   #to select the vertex if correct
else:
loop.vert.select = False  #a good addition. sometimes all vertices are selected from the beginning


So the trick is convertig it to a bmesh and go through that bmesh. After everything is done, just throw it back to the bpy-mesh:

bm.to_mesh(obj.data)


And if you change the view to edit-mode you will notice that all the (in this case white) vertices are selected while the rest is deselected. Just make sure your object is in object-mode. At least, when giving returning the bmesh back to your mesh.

(And for all the newbies: "obj.data" stands for "bpy.data.objects['x'].data", which is of course the mesh of the object :) )

• Default cube each vert belongs to 3 linked faces. The selection of verts using method above will depend on the face order. ie if the last face is not white it will deselect all 4 verts of face, but the 4 adjoining faces could all be white and hence 2 verts of each of those white faces is now deselected. Recommend instead selecting a face based on loop vert colours. Also see blender.stackexchange.com/a/73900/15543 re comparing values, checking for equality is dodgy. Can also be done with bmesh in edit mode. Can be done without bmesh look at mesh color layer. Jan 23, 2021 at 16:01