I made a list of parts to replace to decolor the 10327 Dune Ornithopter (explanation and text version in description)
I made this list based on the instructions PDF that's available from LEGO's website. For most of these, it doesn't really matter if they are black, dark bluish gray or light bluish gray so I picked them based on what will most likely look good with the surrounding colors and what is cheapest on Bricklink.
In general, if you want to save a few bucks, you can probably leave all tan and white pieces as they are. For me, the complete replacement (250 pieces) cost about 35€ plus shipping.
Count
Number
Name
Original
Replacement(s)
2
6346389
Technic, Axle and Pin Connector Perpendicular Double Split, Reinforced Sides
White
Dark Bluish Gray
5
6058177
Brick, Modified 1 x 2 with Studs on 1 Side
White
4x Dark Bluish Gray, 1x Black
6
6289797
Technic, Axle 2L with Pin without Friction Ridges
White
Light Bluish Gray
4
4208160
Technic, Liftarm Thick 1 x 3
White
Black
2
6370532
Technic, Axle and Pin Connector Perpendicular Double with Axle Connector 2L
White
Not available
10
371001
Plate 1 x 4
White
6x Dark Bluish Gray, 4x Light Bluish Gray
2
6360069
Technic, Liftarm Thin 1 x 5 - Axle Holes
White
Light Bluish Gray
2
389401
Technic, Brick 1 x 6 with Holes
White
Black
2
6001831
Technic, Liftarm Thick 1 x 9
White
Dark Bluish Gray
4
6013938
Technic, Pin 3/4
Tan
Dark Bluish Gray
6
4666579
Technic, Axle 1L with Pin without Friction Ridges
Tan
Light Gray
1
6117975
Bracket 1 x 2 - 2 x 2
Tan
Dark Bluish Gray
8
4121921
Plate 1 x 3
Tan
4x Dark Bluish Gray, 2x Black, 2x Light Bluish Gray
4
4118790
Plate 2 x 3
Tan
Dark Bluish Gray
4
4201062
Brick, Modified 1 x 4 with Studs on Side
Tan
2x Dark Bluish Gray, 2x Black
5
4550323
Arch 1 x 4
Tan
Black
2
4550324
Tile 1 x 4
Tan
Black
1
6186258
Slope 45 2 x 4
Tan
Dark Bluish Gray
2
4143409
Plate 1 x 10
Tan
Dark Bluish Gray
7
6271820
Technic Bush
Red
Light Bluish Gray
30
6378120
Technic, Pin 1/2 with Friction Ridges
Red
Dark Bluish Gray
20
6360104
Technic, Pin with Friction Ridges and Tow Ball with Round Pin Hole
Red
Black
2
6384112
Bar 1L with 1 x 1 Round Plate with Hollow Stud
Red
Black
31
4142865
Technic, Axle 2L Notched
Red
Black
7
300421
Brick 1 x 2
Red
4x Dark Bluish Gray, 3x Black
1
6385920
Technic, Brick Modified 1 x 2 with Hole and 1 x 2 Plate
Red
Light Bluish Gray
2
6271827
Technic, Liftarm, Modified Bent Thick L-Shape 2 x 4
Because the general consensus among pretty much all reviewers was that it’s a great set but the colored pieces (especially the blue and red technic pins) look very ugly in an otherwise monochrome set.
Some of the pieces on the inside may not need to be replaced but because I don’t have the set here yet I can’t tell which ones are visible from the outside and which ones aren’t so I included all of them.