I'm just wondering if there was a reason why `$base` was excluded from the example code?
I feel like it would be helpful to display how the code needs to be written with `$base` included. It was a little confusing to me at first and I'm sure I'm not the only one who was unclear.
I would change:
color-pick-contrast($base, ($color1, $color2));
Also, maybe this is overkill but I don't think it would hurt to define `$base` in the parameters table.