This seems to be working now.
convert -size 1x1 xc:"hsl(180,50%,50%)" txt:-
# ImageMagick pixel enumeration: 1,1,65535,rgb
0,0: (16384,49151,49151) #4000BFFFBFFF rgb(25.0004%,74.9996%,74.9996%)
gives the correct rgb colors at 25%,75%,75%
Also
convert -size 1x1 xc:"hsla(180,50%,50%,0)" txt:-
# ImageMagick pixel enumeration: 1,1,65535,rgba
0,0: (16384,49151,49151,65535) #4000BFFFBFFF0000 rgba(25.0004%,74.9996%,74.9996%,0)
is reporting rgba correctly at 25%,75%,75%,0
Thanks