The reduction is computed in polynomial time by one word RAM program, the compilation of the IMP+ program that reads the length-prefixed word into an array, decides in one linear pass whether the word has the shape of an encoding, and, if it does, writes the word of the multicoloured graph with the passes of the fixed-parameter program; on every other word it writes nothing. The run costs at most $16300 (bitSize x + 1)^3$ instructions when the word length fits the values, all of which are below $(|x| + 2)^4 + max x + 1$.