CMYK Gradients in InDesign
Creating a nice, smooth gradient in RGB is easy – with plenty of colours in the range getting a subtle transition from one colour to the next requires little in the way of thinking. With CMYK for print however, things are quite another matter…
First of all, the colours that fall within the printable range are considerably less than RGB. Also, most of the print-based colours don’t have the vibrancy of RGB screen colours, which means they look flatter, duller and sometimes, just plain muddy.
In CMYK, going from one colour to another often leads to ‘banding’ issues, where the lack of depth to the colour gamut becomes apparent. Going from a colour to the default black for example, usually ends up with some dull greys in the middle of the gradient.
This can be avoided by looking at the cyan, magenta, yellow and black breakdown in your base colour and creating a ‘rich’ black based on this. For example, going from a violet with 79, 81, 0, 0 to black I would create a black of 80, 80, 0, 100:

Rich Black
Using this new rich black or a colour that has been modified to transition from our base colour, we can achieve a much nicer and certainly smoother CMYK gradient like this:

Smoother Gradient
How about when you are transitioning from one color to another (not black) I get these weird “gray looking” shades in the middle
Add an intermediate colour stop using values from the colours on either side. Same technique as going from colour to black.