adic←{⎕IO←0         ⍝ Bijective base-⍺ numeration.

    b←⍬⍴⍴a←,⍺       ⍝ base and alphabet

    1=⍴⍴⍵:b⊥1+a⍳⍵   ⍝ vector: decode digs → number
                    ⍝ scalar: encode number → digs
    1=b:⍵/⍺         ⍝ unary: special case
    n←⌊b⍟1+⍵×b-1    ⍝ number of digits
    z(¯1+b*n)÷b-1  ⍝ smallest integer with length n
    a[(n/b)⊤⍵-z]    ⍝ digits from alphabet ⍺.
}
code_colours

test script

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