code: def _interpolate_axis(self, axis, v):
      i = self._find_interval(v)
      v = rinterpolate(self.intervals[i - 1], self.intervals[i], v)
      return interpolate(
          self.colors[i - 1][axis], self.colors[i][axis], v
      )
  
imports: from sympy.core.basic import Basic
  from sympy.core.symbol import Symbol, symbols
  from sympy.utilities.lambdify import lambdify
  from .util import interpolate, rinterpolate, create_bounds, update_bounds
  from sympy.utilities.iterables import sift
label_desc: Use image node_id 4 for calling the ColorGradient obj's underlying member method code with example usage: obj._interpolate_axis(axis, v) and returns: interpolate