Hi Adam Pleshkewych ,
We can achieve your requirement using "index()" function.
We get the Serial Numbers as out put for Index() function, So we can create Calculationms like below
if index() = 1 then "Green"
elseif index() = 1 then "Blue" ====================
elseif index()> 20 then "1Color" end
Then We can drag the above calculated field into Colors shelf, then assign the colors accordingly.