Add Color.scala to black list (scala#21717)

Add Color.scala to black list

The test added in scala#20356 seems to break `test_scala2_library_tasty`, due
to a [problem](scala/bug#13009) in Scala 2
library.

[test_scala2_library_tasty]

Author: liufengyun

compiler/test/dotc/neg-init-global-scala2-library-tasty.blacklist

@@ -18,3 +18,4 @@ global-list.scala
 t5366.scala
 mutable-read7.scala
 t9115.scala
+Color.scala