I often wonder about these questions.
The questions seem to be divided into two types:
Questions about whether newts can see colour and how their brains function seem like scientific questions and are probably fairly easy to answer. Wikipedia says that newts can see colour, and indeed that some reptiles and amphibians may have more acute colour sensitivity than mammals:
Color vision - Wikipedia, the free encyclopedia
Questions about how newts think (and whether they have fun) are perhaps in a different category; one is essentially asking: what it is like to be a newt?
Wondering about this question several months ago, I was doing some reading on the problem on consciousness in general and ran across this interesting paper by a philosopher named David Chalmers:
Facing Up to the Problem of Consciousness
Facing Up to the Problem of Consciousness
This is apparently a seminal paper in the field exploring questions of consciousness. It does not answer the question of what it is like to be a newt (no one knows!) but it does give some insight into the problems that one encounters when trying to answer that type of question. Chalmers points out that despite great advances in understanding how brains (and organisms in general) work, we really have no idea why the structure and experience of an organism gives rise to a particular conscious experience.