Ran into this the other day, had stored the color assignments for a set of features as Hex so I could easily drive Symbol color, but then wanted that color available in the label class was well. There is a `ToHex` function in Arcade, but no reverse `ToDec` function. Luckily it's not that difficult to implement this by hand:
var hexMap = {'0':0, '1':1, '2':2, '3':3, '4':4, '5':5, '6':6, '7':7, '8':8, '9':9, 'a': 10, 'b': 11, 'c': 12, 'd': 13, 'e': 14, 'f': 15}
function HexToDec(code) {
var val = 0
code = Reverse(Split(code, ''))
for (var part in code) { val += (Pow(16, part)) * hexMap[code[part]] }
return val
}