Hi, and first of all, thanks for what you told me.
This time I've tried to use different amount of time between the frames, and I also tried to adjust the colors, but I have little problems:
Maybe You can help me 
How can I see all the frames:
I mean when I draw something and I chose how many frames tha image will be made of I can see only the first one, the others are below and of course I can work on them but I never have the global situation under my control.
It will be great to see all the frames one near the other, like a cinematic sequence.

I would like to use the exact palette fo a generic gba game, where is possible to find it?
Thanks again, I will try to use your advices in my further project.
Matteo