match the array content

H!

How do I do this ??

a$(0) = "red"
a$(1) = "blue"
a$(2) = "red"
a$(3) = "green"
a$(4) = "purple"
a$(5) = "purple"
a$(6) = "purple"

now I want to know that red is at place 0 and 2
and purple at place 4,5,6

I was testing things but that fails:

aantal = 7
Dim a$(aantal)

a$(0) = "red"
a$(1) = "blue"
a$(2) = "red"
a$(3) = "green"
a$(4) = "purple"
a$(5) = "purple"
a$(6) = "purple"

For i1=0 To aantal

	For i2=0 To aantal
	
		If i1<>i2 Then
		
		;	If a$(i1)=a$(i2) Then
;
;			Else

;			EndIf
			
		EndIf
		
	Next
	
Next

Thanks,
GC-Martijn