John (J5) Palmieri has wrote an excellent suggestion for Echo team:
Full color icons bellow 32x32 never look good and almost triple the
amount of work an artist needs to do instead of creating beautiful icons
at higher resolutions. Working with two toned OLPC icons I can say
simple icons look great at low resolution and often can mix with any
theme as long as the shapes are similar. What I suggest is to explore
doing black and white or gray scale for smaller icons and use the full
color icons where they would have the most impact.