text: Title: Bug Report: Alpha setting with Panel not working
  Body: **Describe the bug**
  When Adding a plot mpf.make_addplot((df['SPY']),color='black',alpha=0.3,panel=0) the Alpha Setting is not reflected once Panel number is assigned. The line remains a solid black.
  
  **To Reproduce**
  Steps to reproduce the behavior:
  1. Add Panel_ratios and num_panels to mpf.plot
  2. Add apds = [mpf.make_addplot((df['SPY']),color='black',alpha=0.3,panel=0)]
  3. Add addplot = pads to **kwargs
  
  **Expected behavior**
  Alpha setting to work
  
  **Screenshots**
  None