I'm kind of confused, but maybe this will help:

Option Explicit
Sub testme()
   Dim myBaseCell As Range
   Dim myCell As Range
   Dim myRng As Range
   Dim myColorIndex As Long
   
   Set myBaseCell = Nothing
   On Error Resume Next
   Set myBaseCell = Application.InputBox(Prompt:="select your cell", _
                         Type:=8).Cells(1)
   On Error GoTo 0
   
   If myBaseCell Is Nothing Then
       Exit Sub 'user hit cancel
   End If
   
   myColorIndex = myBaseCell.Interior.ColorIndex
   
   For Each myCell In Worksheets("sheet1").UsedRange
       If myCell.Interior.ColorIndex = myColorIndex Then
           If myRng Is Nothing Then
               Set myRng = myCell
           Else
               Set myRng = Union(myCell, myRng)
           End If
       End If
   Next myCell
   
   If myRng Is Nothing Then
       MsgBox "No cells found"
   Else
       MsgBox "Found here: " & myRng.Address(0, 0)
   End If
   
End Sub