Slightly change curve color hue between adjacent channels

[HGSilveri]

With the changes made in #385 , sequence drawing will omit the detuning curve when it is not being used. This results in more compact plots, but it also make the curves harder to tell apart at a glance. I propose we slightly change the hue between adjacent channels to make them easier to tell apart. I think a cycle of two or three distinct colors should be enough, something like this:

And although the problem is not so prevalent when curves other than the amplitude are drawn, I think we can still change the hue of the other curves out of consistency.

I'm doing these changes through slight increments in the hue (the H) in the HSV color space. The full resulting color palette is the following: