I can confirm a possible problem when modulating saturation in HCL colorspace, where some white parts become black. It does not go away in HDRI mode
see topic viewtopic.php?f=1&t=22243
Input:

HCL mode: (see small black square in middle of limo)
convert wedding_party_sm.jpg -define modulate:colorspace=HCL -modulate 100,80,100 wedding_party_sm_hcl_h80.jpg

HSL mode: (fine)
convert wedding_party_sm.jpg -define modulate:colorspace=HSL -modulate 100,80,100 wedding_party_sm_hsl_h80.jpg

HSB mode: (fine)
convert wedding_party_sm.jpg -define modulate:colorspace=HSB -modulate 100,80,100 wedding_party_sm_hsb_h80.jpg
