Overlaying a FK5 FITS image as contours on top of a ICRS FITS colorscale image (with aplpy)

I am trying to use Aplpy to plot a colorscale image and overlay another FITS image as contours. However, the colorscale-imaged FITS uses ICRS while the contours FITS uses FK5. I found when I am plotting them, the difference in the coordinate system is not corrected.

Is there a way to put both under, e.g. ICRS, to match the coordinate system properly?

Thanks a lot!