Here's the relevant part of the input again. Cells X and Y both have colour 5.

6 6 5 5 5 5
5 5 5 5 5 5
5 5 X Y 5 5
6 6 5 5 5 5
6 6 5 5 5 5
6 6 5 5 5 5

Cell Y has depth 3, but the depth of cell X is only 2 (one step down and one step left get you to a differently-coloured cell). So, X isn't part of the solution.

what's the input?

In what language?

Try printing out your class variables FIRST and SECOND at the beginning of each productFib() function call. Think about what a static class variable is, and how it will work in this context if several tests are run consecutively.

As a side note the issue tag is for issues that you can prove are with the kata itself, not issues you're having solving it. I've resolved this one; please use the question tag in the future for this kind of query.

Please use spoiler flag next time.

What do you mean? According to description:

The longest word will never be greater than this width.