Hello Guys i am having a problem when i apply boolean modifier, the color of the object turns funny, i have been trying to solve this issue for a day. Can any one help me Thank you 
you can see the colors turned dark grey on the sides.
The normals have flipped. Hit crtl+n and it should be normal. Sometimes this doesn’t work for me and I have to find it under the mesh menu, manually select the faces and flip them.
no the normal are fine
that is the problem the normals are fine but the color changed
Sometimes it can be duplicate faces then. Removing doubles does not remove these. Try deleting some faces and see what’s underneath.
There is no facees or anything inside i checked here take a look i removed a face to show you, there is a bone inside.
now i tried to union a full cube and it turned the whole cylinder dark gray.
Okie. Check the vertices for ngons. If there are more than 4 points to the
face then you have ngons. They cause discoloration because blender doesn’t
know how to shade them. Sometimes the edge split modifier can fix it.
No i checked there are no Ngons
I wonder if you could upload the blend file to filedropper.com or the like so we can take a look.
What version of Blender are you using as well? For future reference you can take screenshots with control and F3 and it includes the UI so we can see what is applied etc.
I’ll try to look when i can if the other students dont beat me to it 
here is the link to the file can you please check it, i was having some problem to upload that file on file dropper so, upload it on Uploadfiles. Here’s the link to the file.
Getting the same resut but are you remembering to delete the original cube after making the union as i seem to remember having to do that.
yes try applying the union boolean modifier on it and the color become different idk what is causing this and yes i do remove the cube, the cylinder is whats changing the colors
Okie. Some interesting results.
This is what happened after applying boolean modifier and I disolved the ngon (yes there was some) verticies.
This is after deleting the edges attached to those weird faces.
And the final result of reconstruction.
Honestly, you’re better off just pressing crtl+j to join. It’s the same result.
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I guess i will use that, Everyone thank you so much for helping me I really appreciate it 
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