Convert Magic the Gathering colours to a Colour based deck name
05AB1E, 136 135 133 132 bytes
“ƒÏˆ¨†¾‡—„¸ ŽÌ“#'Î×ì.•вO₁ŸĀ0Ðëœ´0+Eм/#‰TôbHüÆΣÇÐζfβq₅([²åOÇηB₂È¥ƶ]9í$µÅ–tå(h0!Ãα9½êT₄Ì€+µxΩ;'Äçî9©ÙÝ“R_Ÿ U„δ
ÅíÂu•#5ǝ˜.•Iλβ•æé¦Il{kè

Outputs in full lowercase; uses the shortest outputs if multiple are allowed.
Try it online or verify all test cases (uses a random permutations for each test case input).
Explanation:

“ƒÏˆ¨†¾‡—„¸ ŽÌ“ # Push dictionary string &quot;black green red blue white  brown&quot;
 #              # Split it on spaces: [&quot;black&quot;,&quot;green&quot;,&quot;red&quot;,&quot;blue&quot;,&quot;white&quot;,&quot;&quot;,&quot;brown&quot;]
  'Î×ì         '# Prepend dictionary string &quot;mono&quot; to each string
.•вO₁ŸĀ0Ðëœ´0+Eм/#‰TôbHüÆΣÇÐζfβq₅([²åOÇηB₂È¥ƶ]9í$µÅ–tå(h0!Ãα9½êT₄Ì€+µxΩ;'Äçî9©ÙÝ“R_Ÿ U„δ\nÅíÂu•
                # Push compressed string &quot;golgari rakdos gruul dimir simic izzet orzhov selesnya boros azorius jund ana grixis rug abzan dega naya esper bant raka chaos dune witch yore ink domain&quot;
 #              # Split on spaces as well
  5ǝ            # Insert this list at 0-based index 5
    ˜           # And flatten the list to complete the list of deck-names
.•Iλβ•          # Push compressed string &quot;bgruw&quot;
      æ         # Pop and push all its permutations
       é        # Sort them by length: [&quot;&quot;,&quot;b&quot;,&quot;g&quot;,&quot;r&quot;,&quot;u&quot;,&quot;w&quot;,&quot;bg&quot;,&quot;br&quot;,&quot;gr&quot;,&quot;bu&quot;,&quot;gu&quot;,&quot;ru&quot;,&quot;bw&quot;,&quot;gw&quot;,&quot;rw&quot;,&quot;uw&quot;,&quot;bgr&quot;,&quot;bgu&quot;,&quot;bru&quot;,&quot;gru&quot;,&quot;bgw&quot;,&quot;brw&quot;,&quot;grw&quot;,&quot;buw&quot;,&quot;guw&quot;,&quot;ruw&quot;,&quot;bgru&quot;,&quot;bgrw&quot;,&quot;bguw&quot;,&quot;bruw&quot;,&quot;gruw&quot;,&quot;bgruw&quot;]
        ¦       # Remove the first empty string
I               # Push the input-string
 l              # Convert it to lowercase
  {             # Sort its characters
   k            # Get the index of this string in the list of permutations,
                # or -1 if it isn't present in the case of input &quot;c&quot;/&quot;C&quot;
    è           # And use that index to index into the list of deck-names
                # (0-based, where -1 will wrap around to the end)
                # (after which the result is output implicitly)

See this 05AB1E tip of mine (sections How to use the dictionary? and How to compress strings not part of the dictionary?) to understand how the compressed strings work.