title: matplotlib pyplot.show: Invalid RGBA
body: <p>I just need to draw scatter plot in 3D.</p>
  
  <pre><code>from mpl_toolkits import mplot3d
  from matplotlib import pyplot as plt
  ax = plt.axes(projection="3d")
  ax.scatter(dots_x, dots_y, dots_z, c='red')
  plt.show()
  </code></pre>
  
  <p>There dots_x, dots_y, dots_z are coordinates (python lists). Every time I running program I get <code>ValueError: Invalid RGBA argument: (1.0, 0.0, 0.0, 0.300088123161615)</code> </p>
  
  <p>I don't know anything about this tuple. BUT if i use plot3D instead of scatter3D i get perfect curve.</p>
  
  <p>Full error message:</p>
  
  <pre><code>Traceback (most recent call last):
    File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\colors.py", line 166, in to_rgba
      rgba = _colors_full_map.cache[c, alpha]
  KeyError: ((1.0, 0.0, 0.0, 0.300088123161615), None)
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\backends\backend_qt5.py", line 519, in _draw_idle
      self.draw()
    File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\backends\backend_agg.py", line 437, in draw
      self.figure.draw(self.renderer)
    File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
      return draw(artist, renderer, *args, **kwargs)
    File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\figure.py", line 1493, in draw
      renderer, self, artists, self.suppressComposite)
    File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\image.py", line 141, in _draw_list_compositing_images
      a.draw(renderer)
    File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\mpl_toolkits\mplot3d\axes3d.py", line 281, in draw
      reverse=True)):
    File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\mpl_toolkits\mplot3d\axes3d.py", line 280, in &lt;lambda&gt;
      key=lambda col: col.do_3d_projection(renderer),
    File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\mpl_toolkits\mplot3d\art3d.py", line 459, in do_3d_projection
      fcs = mcolors.to_rgba_array(fcs, self._alpha)
    File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\colors.py", line 267, in to_rgba_array
      result[i] = to_rgba(cc, alpha)
    File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\colors.py", line 168, in to_rgba
      rgba = _to_rgba_no_colorcycle(c, alpha)
    File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\colors.py", line 219, in _to_rgba_no_colorcycle
      raise ValueError("Invalid RGBA argument: {!r}".format(orig_c))
  ValueError: Invalid RGBA argument: (1.0, 0.0, 0.0, 0.300088123161615)
  </code></pre>
  
  <p>Sorry for my english :)</p>
  
  <p>UPD: There is entire code of my program</p>
  
  <pre><code>from sympy import *
  from mpl_toolkits import mplot3d
  from matplotlib import pyplot as plt
  import pdb
  
  """
  """
  
  print ("""dx/dt = f(t,x,y,z)
   dy/dt = g(t,x,y,z)
   dz/dt = r(t,x,y,z)""")
  
  x,y,z,t = symbols('x y z t')
  
  f = eval(input("dx/dt = "))
  g = eval(input("dy/dt = "))
  k = eval(input("dz/dt = "))
  
  n = int(input("Input number of dots: "))
  delta_t = eval(input("Input time 'step': "))
  
  t0, x0,y0,z0 = eval(input("Input initial conditions t0, x0, y0, z0: "))
  
  
  dots_x = [x0]
  dots_y = [y0]
  dots_z = [z0]
  current_t = t0
  
  k1,k2,k3,k4 = None, None, None, None
  m1,m2,m3,m4 = None, None, None, None
  j1,j2,j3,j4 = None, None, None, None
  
  for i in range(1,n+1):
      k1 = f.evalf(subs={x: dots_x[i-1], y: dots_y[i-1], z: dots_z[i-1], t:current_t})*delta_t
      m1 = g.evalf(subs={x: dots_x[i-1], y: dots_y[i-1], z: dots_z[i-1], t:current_t})*delta_t
      j1 = k.evalf(subs={x: dots_x[i-1], y: dots_y[i-1], z: dots_z[i-1], t:current_t})*delta_t
  
      k2 = f.evalf(subs={x: dots_x[i-1]+k1/2, y: dots_y[i-1]+m1/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
      m2 = g.evalf(subs={x: dots_x[i-1]+k1/2, y: dots_y[i-1]+m1/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
      j2 = k.evalf(subs={x: dots_x[i-1]+k1/2, y: dots_y[i-1]+m1/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
  
      k3 = f.evalf(subs={x: dots_x[i-1]+k2/2, y: dots_y[i-1]+m2/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
      m3 = g.evalf(subs={x: dots_x[i-1]+k2/2, y: dots_y[i-1]+m2/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
      j3 = g.evalf(subs={x: dots_x[i-1]+k2/2, y: dots_y[i-1]+m2/2, z: dots_z[i-1]+j2/2, t:current_t+delta_t/2})*delta_t
  
      k4 = f.evalf(subs={x: dots_x[i-1]+k3/2, y: dots_y[i-1]+m3/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
      m4 = g.evalf(subs={x: dots_x[i-1]+k3/2, y: dots_y[i-1]+m3/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
      j4 = g.evalf(subs={x: dots_x[i-1]+k3/2, y: dots_y[i-1]+m3/2, z: dots_z[i-1]+j3/2, t:current_t+delta_t/2})*delta_t
  
      dots_x.append(dots_x[i-1]+(1/6)*(k1+2*k2+2*k3+k4))
      dots_y.append(dots_y[i-1]+(1/6)*(m1+2*m2+2*m3+m4))
      dots_z.append(dots_z[i-1]+(1/6)*(j1+2*j2+2*j3+j4))
      current_t += delta_t
  
  print (dots_x)
  print (dots_y)
  print (dots_z)
  
  plt.switch_backend(u"qt5agg")
  ax = plt.axes(projection="3d")
  # pdb.set_trace()
  ax.scatter(dots_x, dots_y, dots_z, c='red')
  plt.show()
  </code></pre>
  
  <p>Sample input:</p>
  
  <pre><code>dx/dt = y - x 
  dy/dt = x*(28-z) - y 
  dz/dt = x*y - z 
  number of dots: 500 
  time step: 0.1 
  initials: 0, 1, 1, 1 
  </code></pre>