One thing liquids just can't do is bleach AND contain enzymes.
Since enzymes are usually more important than bleaching, basically all liquids contain enzymes.
To offset the reduced cleaning ability due to that fact, they often contain more enzymes (both in type and amount) and surfactants (tensides, again both type and amount).
Further they often contain different kind of water softeners.
That in general means they are better at removing non-bleachable stains (oils, fats, particulates) and less likely to leave visible residues on colors.
Further they can't bleach colors. Some might contain optical brighteners though, which might shift perceived colors. But those can always be washed out again.
Powders however can contain both enzymes and bleaching compounds. And more often actually do since you get better cleaning for cheaper that way.
Thus the risk accidentally using a detergent that might permanently shift colors is higher.
Further they often contain water softeners that aren't as easily rinsed out.
That on the other hand means they are better for some stains (like blood, food with strong colors etc) and only really good way for whites to stay whites.
But for colors and general washing, a liquid might be a safer choice.