Add removal note

dstansby · dstansby · commit 02e1396ffd55 · 2020-07-26T10:18:17.000+01:00
diff --git a/doc/api/next_api_changes/removals/18069.DS.rst b/doc/api/next_api_changes/removals/18069.DS.rst
@@ -0,0 +1,5 @@
+Removed support for single color strings in `~.colors.to_rgba_array`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Converting a string with single color characters (e.g. ``'rgb'``) in
+`~.colors.to_rgba_array`is no longer supported. Instead, the colors can be
+passed individually in a list (e.g. ``['r', 'g', 'b']``).
