I did a colour count on the diamond sword and got, what, 24 or 27 colours? Regardless, that's a lot of unnecessary colours that aren't even distinguishable in this piece. However, the main problem that I have with these are that they lack shape - that is to say, they look very flat (and dull). I did an edit on the diamond sword with 10 colours used, and tried to make it pop out more:
The lighting is quite arbitrarily done, maybe (I'm lazy). But I mainly wanted to show how you could make the shape stand out more, even with fewer colours. What's important is contrast. Especially with small objects like these, where every pixel is important and must be used to convey as much as it possibly can.
Other than that, I think you've got a pretty cool looking sword. It just needs to stand out more.