Question Masking two-pass shader with another shader?

Hi,
I want to achieve an effect that the object with my shader will have different color when it overlaps (like HERE) AND it will be possible to visualize that mesh only when it is above some other irregular shape (like HERE) - the rest of mesh should be not rendered at all OR (chosen by user in the runtime) rendered with another distinguishable color. The problem is that when I 'merged' those found 2 solutions the effect is not as assumed. The full problem I have described extensively HERE - but not response was given so far.

Could you please give me any hint how to achieve that?