code: def process(self, expression):
          
          a, o, b = expression
          c1 = self._hextorgb(a)
          c2 = self._hextorgb(b)
          r = ['#']
          for i in range(3):
              v = self.operate(c1[i], c2[i], o)
              if v > 0xff:
                  v = 0xff
              if v < 0:
                  v = 0
              r.append("%02x" % int(v))
          return ''.join(r)
docs: Process color expression
          args:
              expression (tuple): color expression
          returns:
              str