Relax assertions on colors

As dominant colors are not stable on different environments

test/support/color_helpers.ex

@@ -0,0 +1,12 @@
+defmodule MusicLibrary.ColorHelpers do
+  @doc """
+  Returns true if the given string is a valid lowercase hex color code.
+
+      iex> MusicLibrary.ColorHelpers.color_hex?("#d3b696")
+      true
+
+      iex> MusicLibrary.ColorHelpers.color_hex?("not a color")
+      false
+  """
+  def color_hex?(value), do: String.match?(value, ~r/^#[0-9a-f]{6}$/)
+end