Suppose three persons are A , B, C.

Now A sees both B and C face colored and both are laughing.

Now A thinks that if My(A’s) face is not colored and B is laughing seeing C,So from B’s perspective he sees  C laughing and A’s face not colored that means his face (B’s) is  colored so B should have stopped laughing soon.
But B continue to laugh that means he thinks that C laughing at A.So A’s face should be colored.

So as soon as he realize he will stop laughing

Possibile situations: 1) First of all, if there was one only guy painted, he wouldn’t see any face painted, so he wouldn’t laugh in the first place. 2) If two guys were painted, they would both laugh for a moment but they would immediately realize that they were both painted (since the 3d guy is not painted) and stop laughing. 3) If they were all painted, it would take just a little longer for them to realize that (than in case 2) and stop laughing.

If there was only one person colored he will see 2 not colored so he wouldn’t laugh. If there are 2 colored persons then each of them sees one colored and one clean. So he will think: if I’m also clean than we both laugh at the colored person, but why does the colored person laugh too? that means that he also sees a colored person so that means I’m colored too, so he’ll stop laughing and so will the other colored person. the final state will be that the clean person will keep on laughing and the other two will stop after a short time. In case all of them are dirty than the process will go like this: I thing that I’m clean and so does the person next to me, but since he sees that  the 3rd person keeps laughing he understands the he is colored too. that brings us to the 2nd option that if there were 2 colored and one clean they will stop laughing. If they don’t stop that means I’m colored too. So at that point they will all stop laughing.