How to compare colour values in Blender using Python?

Question

I have scripted materials on some objects, now I want to make a simple if/else-comparison like this for only (1,1,1)-white material:

if (mat1.diffuse_color == (1,1,1)):
  # do something
else:
  # do something other

printing the color to the console gives me:

<Color (r=0.0000, g=0.0000, b=2.5000)>

I tried several ways but nothing worked, as you can see in my screenshot I must detect the white cubes by comparison their material-colour to white.

Thanks for any help on this!

Edit: I read the API

Answer 1

Basically it's only possible to compare equal data types. By using python's built-in type() method on Material.diffuse_color the console yields it's an instance of the class Color:

>>> type(bpy.data.materials.get("Red-Material").diffuse_color)
>>> <class 'Color'>

Probably the simplest way is to access its 'components' by class attribute Material.diffuse_color.r or index operator Material.diffuse_color[0] and compare the values:

# Check if the red component is 1.0 via equal operator
>>> bpy.data.materials.get("Red-Material").diffuse_color.r == 1 
>>> True 
>>> bpy.data.materials.get("Red-Material").diffuse_color[0] == 1 
>>> True

However, you can also compare two class instances:

>>> mat1_diff = bpy.data.materials.get("Red-Material-I").diffuse_color
>>> mat2_diff = bpy.data.materials.get("Red-Material-II").diffuse_color
>>> mat1_diff == mat2_diff
>>> True

Means that you can create a custom color (class instance) via mathutils module to compare with:

>>> import mathutils
>>> my_red_color = mathutils.Color((1.0, 0.0, 0.0))
>>> type (my_red_color)
>>> <class 'Color'>
>>> isinstance(my_red_color, Color)
>>> True
# Compare color instance with diffuse color
>>> bpy.data.materials.get("Red-Material").diffuse_color == my_red_color
>>> True

Answer 2

Can treat Color values akin to Vector.
The following example, subtracts two colors, normalized to [0, 1], from each other. The result is converted to a vector. If the length of the resultant vector is less than some tolerance then the colors "match".

import bpy
from mathutils import Vector, Color

def color_match(col1, col2, tol=0.001):
    ''' 
    Return true if vector col1 is within tol of vector col2
    '''
    def vector(col):
        # sanitize range (-2, 3, 5) = (0, 1, 1)
        return Vector([max(0, min(1, c)) for c in col])

    d = vector(col1) - vector(col2)
    return d.length <= tol

# test code
white = Color((1, 1, 1))

# comparing instances 
Color((1, 1, 0.999999)) == white
# False

# same again using color_match no tol
color_match(Color((1, 1, 0.999999)), white, tol=0)
# False

# with default tol
color_match(Color((1, 1, 0.999)), white)
# True

color_match(Color((1, 1, 0.995)), white)
# False

# shorthand
color_match((1, 1, 1), white)
# True

Suggest always use some tolerance test (fabs(x - y) < tol) when Comparing Floating Point Values . An example in test code above is

Color((1, 1, 0.999999))

which is NOT equal to

Color((1, 1, 1))

when it may be more desirable that they are treated as equal (or close enough).