Technically a morph always uses 4 colors: head start, head end, tail start, and tail end. If you select less than 4 then we try to make smart choices. If you only choose 1 color then that is assigned to all 4. If you choose 2 colors we assign the first color to the two head colors and the second color to the two tail colors. If you select 3 colors we assign the first color to the two head colors, the second color to the tail start color, and the third color to the tail end color. If you select 4 colors its a 1:1 mapping. Only the boxes with checkmarks feed colors to the palette choices.