Strange grey areas in gradient

I'm sorry if this has been asked before, I couldn't find it.

I was trying to make a rainbow gradient, but between the darker, blue colors there is some strange grey area that doesn't seem to make any sense.

Also the other colors do not seem to be very smooth either, even though the gradient colors are all evenly spaced. Is there any way to make that more smooth (like it would be if I used the blend tool, for example)

The first gradient has been created with the gradient tool, whereas the second with the blend tool.

I am working with the latest version of Adobe Illustrator CC, and in RGB colors.

Thanks in advance!