Compare two columns in two tables

See the working here for Table1 - Open a blank query - Home - Advanced Editor - Remove everything from there and paste the below code to test

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjQyUtJRckksSwVSvol5iempRUqxOiAJY7BIUWYikHZ29YeKmoB4iUU5QCo4MSe1GCpsClZcUgKk3BOLUlLz4MaYg1TmZpZkwHTkJuYpxcYCAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [ID = _t, Name = _t, Role = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"ID", Int64.Type}, {"Name", type text}, {"Role", type text}}),
    #"Merged Queries" = Table.NestedJoin(#"Changed Type", {"ID", "Name"}, Table2, {"ID", "Name"}, "Table2", JoinKind.LeftOuter),
    #"Expanded Table2" = Table.ExpandTableColumn(#"Merged Queries", "Table2", {"Colour"}, {"Colour"}),
    Custom1 = Table.ReplaceValue(#"Expanded Table2",each [Colour],each if [Colour]=null or [Colour]="" then "Unknown" else [Colour],Replacer.ReplaceValue,{"Colour"})
in
    Custom1

 In case, you need code for Table2

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjQyVtJR8k0sykwE0u5Fqal5SrE6IHETIN+nNLkSSDnllKZCRY2AXJfEslQgFZSaAhU0BRtRUgKklGJjAQ==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [ID = _t, Name = _t, Colour = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"ID", Int64.Type}, {"Name", type text}, {"Colour", type text}})
in
    #"Changed Type"