def to_valid_rgb(t, decorrelate=False, sigmoid=True):
  """Transform inner dimension of t to valid rgb colors.
  
  In practice this consistes of two parts: 
  (1) If requested, transform the colors from a decorrelated color space to RGB.
  (2) Constrain the color channels to be in [0,1], either using a sigmoid
      function or clipping.
  
  Args:
    t: input tensor, innermost dimension will be interpreted as colors
      and transformed/constrained.
    decorrelate: should the input tensor's colors be interpreted as coming from
      a whitened space or not?
    sigmoid: should the colors be constrained using sigmoid (if True) or
      clipping (if False).
  
  Returns:
    t with the innermost dimension transformed.
  """
  if decorrelate:
    t = _linear_decorelate_color(t)
  if decorrelate and not sigmoid:
    t += color_mean
  if sigmoid:
    return tf.nn.sigmoid(t)
  else:
    return constrain_L_inf(2*t-1)/2 + 0.5