Do you mean you went through the proof and verified it, or falsified it?

As I understand it, it goes something like this:

...

You have a set of n horses.

Assume a set of n horses are the same color.

Now you also have a set of n+1 horses.

Set 1: (1, 2, 3, ... n)

Set 2: (2, 3, 4, ... n+1)

Referring back to the assumption, both sets have n horses in them, Set 2 is just incremented forward one, therefore, Set 2's horses are all one color, and Set 1's horses are all one color.

Finally, Set 1 and Set 2 always overlap, therefore that the color of all Set 1 and Set 2's horses are the same.

...

So, if you hold the 'all horses in a set of size n horses are the same color' assumption as an actually valid assertion, for the sake of argument...

This does logically hold for Set 1 and Set 2 ... but only in isolation, not compared to each other.

The problem is that the sets do not actually always overlap.

If n = 1, and n + 1 = 2, then:

Set 1 = ( 1 )

Set 2 = ( 2 )

No overlap.

Thus the attempted induction falls apart.

Set 1's horse 1 could be brown, Set 2's horse 2 could be ... fucking purple... each set contains only one distinct color, that part is true, but the final assertion that both sets always overlap is false, so when you increment to:

Set 1 = ( 1, 2 )

Set 2 = ( 2, 3 )

We now do not have necessarily have the same colored horse 2 in each set, Set 1's horse 1 and 2 would be brown, Set 2's horse 2 and 3 would be purple.

...

I may be getting this wrong in some way, it's been almost 20 years since I last did set theory / mathematical proof type coursework.