Just a little arranging around. You do know how to use RGB, don't you?

R = Red
G = Green
B = Blue

Code:
Private Sub BlackToBlue(frm As Form)
    For i = 255 To 0 Step -1
        DoEvents
        For x = 1 To 50000
        Next x
        frm.BackColor = RGB(0, 0, i)
    Next i
End Sub

Private Sub BlueToBlack(frm As Form)
    For i = 0 To 255
        DoEvents
        For x = 1 To 50000
        Next x
        frm.BackColor = RGB(0, 0, i)
    Next i
End Sub

Private Sub BlackToRed(frm As Form)
    For i = 255 To 0 Step -1
        DoEvents
        For x = 1 To 50000
        Next x
        frm.BackColor = RGB(i, 0, 0)
    Next i
End Sub

Private Sub RedToBlack(frm As Form)
    For i = 0 To 255
        DoEvents
        For x = 1 To 50000
        Next x
        frm.BackColor = RGB(i, 0, 0)
    Next i
End Sub

Private Sub BlackToGreen(frm As Form)
    For i = 255 To 0 Step -1
        DoEvents
        For x = 1 To 50000
        Next x
        frm.BackColor = RGB(i0, i, 0)
    Next i
End Sub

Private Sub GreenToBlack(frm As Form)
    For i = 0 To 255
        DoEvents
        For x = 1 To 50000
        Next x
        frm.BackColor = RGB(0, i, 0)
    Next i
End Sub

'etc.
'etc.