Array parameters are specified as individual elements in the URL.
As part of the Lettering option, a palette can be specified using the Palette[] array. If you wanted to specify 2 palette items, then you would use:
Lettering?Text=ABC&Palette[0]=ff0000&Palette[1]=0000ff
The order of the items does not affect the result. So the following is equivalent to the above example:
Lettering?Text=ABC&Palette[1]=0000ff&Palette[0]=ff0000
Gaps cannot exist in the item indexes, so if you wanted to specify Palette[1], then Palette[0] must also be specified otherwise Palette[1] will be ignored. The following example, Palette[3] is ignored because Palette[2] is not included.
Lettering?Text=ABC&Palette[1]=0000ff&Palette[0]=ff0000&Palette[3]=00ff00
When Rendering or Generating a Template, if you wanted to set a different Recipe for specific Elements in the Template
Render/Templates/Design.PXF?ElementRecipe[0].Recipe=Normal&ElementRecipe[0].Element=Text1&ElementRecipe[1].Recipe=Normal&ElementRecipe[1].Element=Text2