Using i and j as normal variables, such as for loop iterators, is bad. Here are some discussions

Over the years, Matlab has been redesigned to carry better performance dealing with i and j as workspace variables, but the ambiguity will never go away.

More: 1 2

Another ambiguous case about complex numbers in Matlab

About "perceptually non-uniform" colormaps: External link one two

Thanks to Ander Biguri for these references.