OLE_COLOR is not defined in Jabaco.
RichTextBox.BackColor is of type "long". You can use "RGB(r, g, b)" to set such a color.
There are 143 hits on "color" if you consult the search facility of this forum.
Give it a try!
Calling external DLLs is one of the more involved areas of Jabaco.
It might be easier to go for the Java way rather than exploiting all sorts of tricky Microsoft APIs.
Happy experimenting!
A1880