This was the easiest one because I could just use
hsl to adjust the hue by a certain step. So we get
hsl(0, 50%, 50%),
hsl(20, 50%, 50%),
hsl(40, 50%, 50%)
Then, I thought of iterating over the saturation to brighten or darken the colors. So I iterated again, adding in 10 to the value, but there was always grey at the start of every color.
Tweaking the loop gave me this final palette:
Not the best, but OK by my standards