calibration of two brands of monitor

I have a formac lcd screen as my primary display and have just purchased a secondhand apple studio display to use as secondary.

The studio display has a distinctly yellow cast compared to the blue cast of the formac.

I've tried calibrating them both but the difference in colour balance remains. I know colour calibration is a big problem for all designers, but can anyone point me in the direction of a free and foolproof method.

thanks in advance