The problem is that darken function requires a color as first argument and, instead, you’re trying to pass a string.
type-of(#6B46C1); // returns color
type-of("#6B46C1"); // returns string
So you should remove all quotes in $innerPagesBgColors
:
$innerPagesBgColors: #6B46C1, #2980B9, #FD5456, #000;