Question: Trouble with colorscheme option

Dear Sir(Madam) 

I plot a spacecurve,which is an intersection of two surface,x+y+z=5 and x*y+y*z+z*x=0.The curve is shown below.

Then I want the curve's color changes accroding to the value of x*y*z.From the help page,I learn that the colorscheme option can make the color of different parts of a surface change accroding to the value of an user given function.However,it does not apply to all Plots' package command.You need to use the display command,colorscheme option with the option "overrideoptions",to force the graph's color to changed to desired.

P1 is the graph of the curve.

The first code works well,it is just a test.

display(P1,colorscheme=["Orange","Blue"],overrideoptions)

The second code fail to chage color(In my document,I use 2-D Math Input,following the example)

display(P1, colorscheme = ["xyzcoloring", proc (x, y, z) options operator, arrow; x*y*z end proc], overrideoptions)

This is the trouble I encountered.So,please help me use this option correctly,or is there any other way to achieve my goal?

Thank you in advance.

The file here.

problem_with_colorscheme_option.mw