Yo lo hago de esta forma
Rutinas.PonFondo_Label(Pta1,248,250,193,248,250,193)
Sub PonFondo_Label(Lbl As Label,Cl1 As String,Cl2 As String,Cl3 As String,Cl4 As String,Cl5 As String,Cl6 As String)
Dim gr As GradientDrawable
Dim Cols(2) As Int
Cols(0) = Colors.RGB(Cl1,Cl2,Cl3)
Cols(1) = Colors.RGB(Cl4,Cl5,Cl6)
gr.Initialize("BL_TR", Cols)
gr.CornerRadius=5
Lbl.Background = gr
End Sub