Coloured avatar silhouettes are called "jelly dolls" in SL. They happen when one of the "avatar render complexity" (ARC), "attachments surface area limit" or "attachments geometry bytes limit" values overshoots the settings configured in your viewer ("Preferences" floater, "Graphics" tab, "Avatars rendering" sub-tab); the values are set to defaults the first time the viewer is launched, depending on your system performances, but you may perfectly change them at any time (setting the three limits to 0 by pulling their respective slider to the left will disable the "jelly dolls" feature entirely).
However, these setting should not affect your own avatar (i.e. the avatar you log into SL with the viewer)... If they do, there's something wrong; in this case, file a proper bug report
, following the bug reporting rules
to the letter (the logs and reproduction steps are needed !).
To learn more about the jelly dolls feature and how it is implemented in the Cool VL Viewer, please refer to this thread