Perhaps not a bug, but the description should really be updated. Looking at some of the blueprints here, seems like I wasn't the only one to be misled by this.
Currently color mixers describe needing 2 buildings per launcher, which leads me to believe a full belt of red and green would need 16 color mixers total and output two full belts, but in reality you need 32 color mixers.
Using the following test BP, my theory was confirmed - 4 color mixers for 1 thrower of red and 1 thrower of blue, were faster than 2 color mixers for the same input.
SHAPEZ2-1-H4sIAHc+z2YA/6yab0/bMBDGv4u1l4mUnPPPkXixwpDYYOpgYqAJoawNEClLUJoMEOp3X9omVVv6J/fEIFVC5Oc723fn85O+i2sR2pZyDTEYivBdfCrfnmMRirNJGmVjYYizUZ7N/nESlZEIf4uk/jscplH5kBd/J8LIqjRdfIjJU/Qch5fV4lfcTQ3xJSuLJJ7U4Lu4rS0Z4lKE0hA/axPn0Vtelfff63Gi9N65p1eq7Q1WvRhUSTpOsketftyIMDDm3vir7pymVTIe5kV5GY/i5F9cnGVlXGRReh0VSZSVtQ/Hs8c+z3+OxNSYD6X0DWXbGseyNI7VzNFr9+1PnJ7ED1GVltsHOH4Z/Lj9lVbj40EZ3Tylo8ej5WDBcqzaL1qMOEye4/P44cNoG+virs5lxpzmxUtUjA9gDoZJDCMMszHMgjC1SW1Z/IukKPIiHi9RatGOpiTzeYf5vMt83mc+vwjUtZi7SF7jYkfkt5iHYe6WMFim61WcjXcl67fNZF2M5AF5X49ytLFcOhzy9TiktDmk9Djkbc+lr1U2KpM82x8gATNxF5TPpALIVtDDFns5FDMt1Y4ye8hOsMoRs2rwzXmYOXcH1qVAex/DuvO2LSibGY6EnCN+i7IcpE0HD2yAWm0zJKvN4K6g1QtzMczBMIlhhGE2hlkQpiAqgCgforAIwQIEiw8sPMDo4FPcE3O9YuxL/YBb331mYVfbV6rb6chdKsUsls2OmFi+mtj+mxJqgdatzfu2qzIvosf4QIcd9MMb6x6zc2AAigs0M1rPjC6XjcY1R1dvbyo9zb0Oj5Qmj4LlbiB9pol1z2bAz/StqdTRSwl1wx+xLn1fsGVjuhcL7DwzscPT9JDG1ubmL3EByQUcLtBUOdvrV2RhvrXvMA/vFYh3iK+A3FsaUKklEldqF9ytediymAdAqVGHlhp1aNKotZPGVwDS5l82yYJ0wtZtZjlsMYlhzCpKhM3N1qXwNSP1VfgIuiISdEUkC5LPyObJZ/RBxd8XowTNn6D5BzuUhn3++ZDIRpg2Ry6GORgmMYwwzMZkTrIwcxYiOjZz41I2T29srPCaW1p7q9nZN2nxX4aSguTGFnMxzMEwiWGEYTaGWRCmICqAKB+isAjBAgSLDyw8wOjgU8D5zX1NQRZw4HcvZN3riYklD1f7I6uXCtcUZxi3QMWsBbGmzsQ6SK4602KKeUDu0pD2BQ2mH5GPYR6GuRjmYJjstWmoYtJmBMxboHjS9FVzkNVZrRGHbx/sBbV77YPHub3PNZlObeKdIQZJFhVv13ExSWbfZJx96XI6vZtO/wsgwABJ7ceCgykAAA==$