The main goal of Tango icon theme is to ensure that the applications don’t appear alien in different desktop environments. So, if a user is running any multiplatform application, he/she should not get the impression that it looks inconsistent and unpolished when he/she switches the environment it is run in. Although this isn’t about the merging of styles of various desktop systems, the main aim is to make sure that the appearance doesn’t seem drastically different in different platforms.

Apart from a generic type fallback, same kind of styling can help in smoothening of the transition phase. Nevertheless, please keep in mind that a few legacy icons may stay on the user’s desktop.

Coming to the color palette aspect, it’s important to have a common color palette to keep the look consistent across different icons. The visual style is greatly impacted by the type of colors used. The Tango project’s color palette comprises of 27 RGB colors, while majority of desktop environments allow for only 24 bit RGB icons.

The normal practice is to use the color palette as a base, spreading it over the large areas, at the time of drawing the icons. Creation of shadows and highlights by changing appropriate values, shading with gradients and making minor saturation changes are endorsed as well as permissible. The colors don’t need to come necessarily from this particular set. Additional colors can also be utilized. What you can do is start from the base color and change the saturation and values, or perhaps even the hue to achieve more consistent results instead of starting with arbitrary colors. Hope you get the drift!