Trying to understand IF Else Statements

Hello,

Can someone take a look at some basic code I wrote and help me figure out what i'm doing wrong.

I would like for a person to enter 2 colors (red, blue or yellow) to make a new color.

If they choose any other color they get an error.

Sub colorMix()

Dim color1 As String
Dim color2 As String

color1 = InputBox("Enter the first color")
color2 = InputBox("Enter the second color")

If Not color1 = "Red" Then
    MsgBox ("You can only enter Red, Blue, or Yellow")
End If

If Not color1 = "Blue" Then
    MsgBox ("You can only enter Red, Blue, or Yellow")
End If

If Not color1 = "Yellow" Then
    MsgBox ("You can only enter Red, Blue, or Yellow")
End If

If Not color2 = "Red" Then
    MsgBox ("You can only enter Red, Blue, or Yellow")
End If

If Not color2 = "Blue" Then
    MsgBox ("You can only enter Red, Blue, or Yellow")
End If

If Not color2 = "Yellow" Then
    MsgBox ("You can only enter Red, Blue, or Yellow")
End If

If Color = "Red" And color2 = "Blue" Then
    MsgBox ("The new color is Purple")

Else

If color1 = "Red" And color2 = "Yellow" Then
   MsgBox ("The new color is orange")

Else

If color1 = "Blue" And color2 = "Yellow" Then
   MsgBox ("The new color is Green")

End If
End If
End If
End Sub

Thank you very much