Worry about using powders for deeply coloured and or dark laundry is residue from insoluble or not totally dissolved solids.
Zeolites aren't soluble which under certain situations can lead to a sort of white "dust" appearing on darker fabrics. Often things going through dryer will remove much if not all of this "lint".
Cheap powders that contain lots of fillers such as cellulose (sawdust),which depending upon various factors can also leave a visible residue on darker coloured textiles.
Powdered laundry detergent formulas have advanced much since 1970's when users were routinely advised to dilute product in hot water before using a cold wash. But there is "cold" water,and there is cold water.
Great thing about liquid detergents for dark or deep coloured things is that you'll likely have less issues with dissolving even if tap cold water is on the chilly side.